Anatomy of the Ignition Switch
 

To start, the diagrams below are specific to the 2000 model year, but should apply to the 98+ trucks. The failure mode is the same for the earlier trucks though.

Quite a while ago, another member had sent me a working, but used ignition switch. I had said at the time that I would dissect it and show everyone how it works or at the very least, what goes wrong. During the disassembly process, I took out one too many screws (:icon_hyper:) and the thing popped apart like an antique clock, springs flying all over the place. :icon_doh: Needless to say, I lost some of them and others I just could not return to their proper positions. So I am not able to discern which position is which (ACC, LOCK, OFF, RUN, START), but I will go through how it works and what goes wrong stages of the discussion.

So... Onto the article:

Anatomy of an ignition switch...

This is such a common problem on many s-series trucks. If weird things start happening with your truck and nothing seems to make any sense the culprit could possibly be the ignition switch.

Ignition switch diagrams:
https://blazerforum.com/forum/attach...ch_sch1of2-gifhttps://blazerforum.com/forum/attach...ch_sch2of2-gif

C211 Connector Views:
https://blazerforum.com/forum/attach...rc211_1of3-gifhttps://blazerforum.com/forum/attach...rc211_2of3-gifhttps://blazerforum.com/forum/attach...rc211_3of3-gif

So how does it all work?

The ignition switch uses a gear that has a few different ramps on either side of it. When you turn the key, the ignition cylinder drives the gear into its different positions. As the ramps pass under each of the small little followers, it acts as a sort of cam that pushes on each of the contact arms. The pictures below do not include any of the gear detents and the main spring on the gear has also been removed (the spring is what pushes the key back after you have started the vehicle).

As you can see, there are five main contacts in the switch. These contacts control everything in the truck. For instance, the large brown wire in the middle/top portion of the switch is the accessory power wire which feeds into the RAP (retained accessory power) relay then off to all the accessory items (radio, windows, etc). The large orange wire is the IGN 3 wire which powers the ABS, HVAC, 4WD, and cruise systems. The large pink wire is the IGN 1 wire that powers the ECM, ENG 1 fuse, O2 sensors, B/U lamps, DRLs, A/C relay, etc.

On the other side, you have the small white wire which feeds the IGN 0 circuit (cluster) and the small yellow wire which feeds into the starter circuit. These two items get power from the small red wire (IGN C fuse) when their respective contacts connect.

Here is a run down of what circuits have power for a given key position (ACC, LOCK, OFF, RUN, & START):

• IGN 0 (small white wire - C1) circuit has power in OFF, RUN, and START -- continuity to IGN C (small red wire - D5)
• CRANK (small yellow wire - D1) circuit only has power in START -- continuity to IGN C (small red wire - D5)
• ACC/RAP (large brown wire - D6) circuit has power in ACC and RUN -- continuity to IGN B (large red wire with white stripe - D2)
• IGN 1 (large pink wire - ) circuit has power in RUN and START -- continuity to IGN A (large red wire - B1)
• IGN 3 (large orange wire - C6) circuit has power in RUN only -- continuity to IGN B (large red wire with white stripe - D2)

So what goes wrong?

Since some of the circuits can have a fairly high current load on them when you start your truck, the arc that happens when the contacts close can be pretty intense. Over time, the contacts will erode/corrode and will loose their conductivity to each other, usually in the form of a higher resistance. This higher resistance also causes heat which further exacerbates the problem.

So what does it all look like?

The first two pictures below are of the two contact sides of the ignition switch. All of the protective covers have been removed and the wiring has been cut short to allow for better photographs.
https://blazerforum.com/forum/attach..._switch_01-jpghttps://blazerforum.com/forum/attach..._switch_02-jpg

The next two photos show the contact arms removed from the switch housing, revealing the contacts themselves and displaying the charring that will eventually cause the switch to fail. I have zoomed in on the contact surfaces showing the most charring on each side.
https://blazerforum.com/forum/attach..._switch_03-jpghttps://blazerforum.com/forum/attach..._switch_04-jpg
As you can see, the IGN 3 contacts are showing the most damage with the IGN 1 contacts starting to show the affects of age as well.

The IGN 3 contacts are the most heavily loaded of all of the contacts in the system and it also is the contact which is opened and closed the most during the life of the truck. Lets look closer at what this contact goes through on a normal start sequence. In a typical start cycle, the key is turned from LOCK, through OFF and RUN, then to START, and finally back to RUN once the vehicle is started. As the key is turned from LOCK to RUN, the IGN 3 contacts close. When the key is then turned to START, the contacts open back up. Once returned to RUN, the contacts close again. This is why it is vitally important to hold the key in the START position until you are sure that the engine is running. The more times you go to the START position, the more life you take away from these contacts.

So what happens when the contacts go bad?

For the 98+ trucks, the most common issue is the "security" light on the dash illuminating. But the problem can also manifest itself as an inoperative fuel pump, unresponsive cluster, ABS and/or SIR lights being illuminated on the cluster, as well as a no start condition (either related to the inoperative fuel pump or a failure of the starter to turn over). The ignition switch can also cause PASSLOCK issues.

All of the pictures and diagrams above are pertinent to the 98+ trucks. The ignition switch found in the 96-97 trucks is quite similar, but the 1st gens and fullsize trucks are very different.

How do I diagnose a bad contact:
On approach to diagnosing ignition switch issues starts by disconnecting the ignition switch harness below the steering column. This requires you to pull off the lower dash knee bolster and reinforcement brace. Once there, you should see the main ignition switch harness connector which is bolted together. Loosen the captive bolt & pull the harness apart.

Testing will be done using a multimeter set to test circuit resistance. Check that your leads read zero resistance when touched to each other before moving on. If they do not, you have a problem with your multimeter, leads, or connections themselves and should find another to use for further testing.

Using the information provided below the connector pinouts concerning the circuit inputs, outputs, and pin numbers, probe each set of contacts & test the resistance in all of the key positions noted. A good contact should have a near zero ohm resistance. If the resistance varies or is over a few ohms, then the contacts are likely compromised. A resistance of even a few ohms can cause the contacts to heat up worsening the condition to the point of excessive voltage drop or all out circuit interruption.

Alternatively, testing on suspect contacts can be performed by back probing the contacts in the main ignition harness with the harness still connected and monitoring the voltage present on each circuit. The voltage should remain the same as the main system voltage. If it wavers or drops out as load is applied through various uses on that circuit (radio, windows, seats, lights, etc.), that contact is most likely compromised.

Voltage drop is another method of testing a live circuit whereby you test for the change in voltage from one side of a circuit to the other. In the case of the ignition switch, you would want to test from the input side of a contact to the output side of that contact and observe the voltage drop. For instance, if you were to back-probe cavity B1 (red wire) and cavity C5 (pink wire) in the ignition switch wiring harness with your multimeter probes, and observe the voltage drop, you could see if there is something out of the ordinary with the IGN1 contacts inside the ignition switch which is responsible for powering a number of critical engine control fuses.

^^^^Each mention of voltage drop in the paragraph above has a link to a separate article discussing the testing of voltage drop & how it can be used.^^^^

*EDIT 28SEP19*
Given the number of weird issues with the cluster that have popped up on the forums recently, I have been revisiting this thread quite a bit and have come up with some new methods for diagnosing these circuits. It occurred to me that there were fuses further down these circuits were we could test for voltage drop so here are a few, easier places to check for voltage drop.

Check the following fuses for voltage through the ignition switch:

• CRUISE fuse 3 (10A) - tests IGN3 circuit - Should have +12V in RUN only - Test voltage drop relative to the IGN B fuse in underhood fuse box
• GAUGES fuse 4 (10A) - tests IGN1 circuit - Should have +12V in START & RUN only - Test voltage drop relative to the IGN A fuse in underhood fuse box
• CLSTR fuse 11 (10A) - tests IGN0 circuit - Should have +12V in OFF (bulb test), START, & RUN only - Test voltage drop relative to the IGN C fuse in underhood fuse box

These three fuses are located in the instrument panel fuse box which is much easier to access than getting at the ignition switch wiring connector with some back-probe pins.

One thing worth noting when testing at the fuses is that the voltage drop may be slightly higher here due to the increased resistance from the additional contact points in the system which may have aged over time (corrosion/tarnish on the fuses and other terminals along the circuit) which might not directly relate to a poor circuit.

Here is an Amazon link to a set of back-probe terminals that I have found extremely helpful in testing connected sealed & non-sealed connections without damaging the seals nor the terminals inside: /end article

I am sure that there are more symptoms as well as information that I have left out. So I would be very pleased for everyone to take a look at this article and ask questions, give their experiences, and let us all know what needs to be added, removed, or corrected.

Thanks and I hope this helps!

Great effort you put into this....good job!!! And here I go and explain what happenened before I changed my Ignition Switch.

About a year ago the car started stalling in the middle of driving. Didnt do it much, but I was concerned. Had it at the dealer and he said that according to his scan tool, it was a bad crankshaft sensor. Changed that and it was good for a while.
Then it started again and let me tell you, it is no fun going 140km/h on the highway and the car quits with no controls whatsoever. Luckily I had made myself used to shifting to "N" and switching on the hazard lights as soon as all the lights went on in the dashboard.
No dealer and no mechanic could tell me what was wrong so I read along these pages some more. The Ignition Switch had always been in the back of my mind, but my mechanic said that makes no sense, so I dropped that idea and went on to changing the EGR Valve. NOTHING CHANGED!!! Oh, I forgot to mention that I still have rough idling at stops...
The stalling got worse and worse. Sometimes only the dash lights were flashing but the car would still run and sometimes it stalled after the controls went beserk!!! It always took a while before I could start it up again. At this time he woul stall about every 4-5 days.

The last 3 weeks though, he would stall on EVERY trip I made. If it was 1km, he would stall once, and it got up to 4 times a day if i made a trip of about 30km. Sometimes he would start right up again and sometimes, as soon as I put him in "D" he would stall.

Last week I ordered a new Ignition Switch (hard to find here, since I am in Germany, but I got it) and put it in on Friday. My mechanic said that this will not solve the problem, BUT... I have been driving about 300km and he has not stalled on me again since. Only thing left is rough idling even after I put in a new Ditributor cap and dist. rotor... But I can live with that...

I took part of the Switch apart since I could not see any burned or loose wires and here is a pic of what I found.


(I would have liked to post a pic here, but I cant!!! I will put it in my album for anyone interested...)

Remove the two screws.

LINK TO overseachevlover's album with more photos of ignition switch contacts.

From the looks of the tarnish on the contact arms, they have gotten hot. I would definitely suspect that the contacts are burnt quite badly.

I took off the screws and added those pics to my album aswell... They are quite burned...

Is there any way to prevent this from happening again???

And, could I just change the contacts and revive the old switch??? (Maybe a silly question, but I like to have spare parts close by...)

You could clean up the contacts and it will likely work in a pinch, but I would not use it long term.

As far as preventing this problem, the less times you have to cycle the key to start your vehicle, the better. I am not sure if there is anything that you can do to reduce the current on the circuit, thereby extending the life, but it may be possible... The IGN 1 circuit powers A LOT of stuff though.

Thank you Kyle for starting this post. My second switch has now also starting giving me problems and I have been kicking around building a test / emergency switch package. This would be a few heavy duty switches along with a push button for the crank signal. This info would help out the folks that either don't have the $$$ for a switch or as in the case of the fellow from Germany could get it up and running fast. I saved the first old switch so I have the bolt on plug and wiring to begin with. Any thoughts on this?

One way that you could reduce the problems with the switch (some of them) is to cut the wiring and install some heavy duty relays in the loop. You would need at least two high current relays to handle IGN 1 and IGN 3. Three relays if you wanted to cover the ACC contacts as well and five relays if you wanted to completely isolate the switch, only requiring low amperage to activate the heavy duty relays (30A minimum).

Now, another thing worth noting with the PASSLOCK system is that there is a problem that has been somewhat left uncured. The PASSLOCK sensor is near the ignition lock cylinder. There is a section of the ignition switch wiring harness that connects to the sensor. Overtime, the contacts tarnish. This can be primarily attributed to the zinc coating that is used on the contacts. When the contacts tarnish, the signal from the sensor to the PCM is affected, resulting in an activated PASSLOCK system and a no start. If waiting 10 minutes allows the vehicle to be started, then the no start is most likely caused by the PASSLOCK system.

There was another post around here somewhere that discussed the PASSLOCK system in more detail... At least I seem to remember one, but it may have been on the content theft deterrent system..

The problem with the ignition in my truck is that the key only works part of the time, and it wont turn to accessory with the key in all the way. It has to put ALMOST all the way in... It seems regardless of which side of the key i insert face up, I always have to take it out and flip it over, reinsert it, and play with it for a few seconds before it will go into accessory.

Solution? My first guess is a tumbler has fallen out of place somewhere..

Definitely sounds like the ignition lock cylinder is worn out, not like an ignition switch problem.

ignition switch problems
 

97 blazer 4x4 just picked this car up cheap, wanted to die some times while running,check engine light started coming on along with faulf codes six of them, two were related to low voltage inputs, five were tranny related codes ,also in limp mode , had to think alot about this one and do a lot of reading ,you guessed it an ignition switch fixed all the problems

OOOHHH! Finally some good reading material!!!

Only issues I have experienced so far are 2 COMPLETE no start conditions. As in, I could not start the vehicle on more than 10 attempts in an hour, or before the battery dies. Whichever comes first.

Kyle, my steering column is still opened up since I went camping back in August. You have just spurred me to dig deeper into mine. Yet, I cannot see how to get the darn thing out.

I'm not exactly willing to spend over $100 on a new switch. How about a NASCAR syle switch system:icon_lolsign:

There should be two ignition switch replacement How-To's posted. The one below is the only one that comes up right now. The other one should be restored shortly...

Ignition Switch Replacement by WolfPack

As far as nascar-esque switches, you definitely could replace the whole ignition switch arrangement with toggle switches. You would just have to remember which ones need to be turned on for which key switch position. All of that is listed above so it shouldn't be too terribly bad. You'd want to still keep the passlock sensor so the key would need to be inserted, but then you could switch the related circuits manually to start the truck. You could even get creative with some relays and design a logic circuit to control them.

That is an interesting proposition!:icon_idea1:

Another possibility where you have trouble turning to accessory is a worn out key. Might be worth trying to have a completely new key cut by a dealer. I had a Saturn that was awful to start-- you had to play around with the key a lot to get it to start or anything. Since the key looked really worn (it was thin on the sides and rounded all over) I had a new key cut before replacing the cylinder. Glad I did because the new keys made the ignition work like a champ.

The switch and the cylinder are two completely different things. The switch is what is being discussed in this thread.

If you cannot turn the key, then it could be either the key or the cylinder. In which case, replacing the key would be the cheapest initial check.

Stabilant 22 is without a doubt the best for this issue in my option.
Every GM vheicle i have had the thrill to work with strange
electrical problems with this type of switch get a treatment of this if not toasted already. (from a power amp hooked up incorrectly)

Not cheap by no means, and never had a comeback to replace switch.

Ive been having a similar problem wit my truck(1987 Blazer).My starter had burnt out from cranking the **** out of it because I had bad gas from sitting for 2 years.When I put on the new starter, the truck will turn over but it wont start.When I turn the key the CEL light wont even come on at all.I'm also not getting power to my Fuel pump.Would a bad ign. switch cause this?

Possibly, but this thread deals specifically with the 2nd gen ignition switches.

For further help on your truck, please create a thread in the appropriate tech section.

My 97 sounds like the fuel pump is getting low voltage (starting to growl a little) but sometimes the wipers work some times not. However today I have got a no start it is getting fuel to the fuel rail but I can take the key to the lock position and remove the key and the fan motor for the a/c still runs. I think it's an ignition switch again the last one was 4 years ago. What a POS

If you are looking for help with your problem, I can move your post to the 2nd Gen Tech section or you could repost this topic there. If you are just making a statement, carry on. LOL

Could the ignition switch cause the instrument cluster to stop working as well as the display on the headboard to show all ------'s instead of gas mileage or temp?? Also, would this make the 4 wheel buttons on the dash to quit working?? Had it to a local small time garage(parts swapper) and they say there are no codes on the computer and they have no idea what is causing it.. Any help would be appreciated.. Thanks...

The ignition switch controls power to a lot of systems in the truck. If you need help diagnosing your problems, you really should post your question in the appropriate technical section. This section is for the discussion of the presented material in terms of additions, corrections, or omissions that may be necessary to make the article more complete.

I hope I'm not bothering this by bumping, but its related.

I believe it was over a year ago I had the same symptoms as already mentioned. Instead of replacing the switch I elected to take it apart and clean the contacts. Just a couple days ago I experienced the same no start/security light issue again. This time I purchased a brand new one and installed it.
When I took the old switch apart last year, for the life of me I could not get that big return spring to go back in, so I ended up with a springless switch. But today, I was able to get it back in. I also noticed, you do not have to take the entire switch apart to clean the contacts.

Aside from already being mentioned about installing relays to reduce the amount of amperage going through the switch, I really see no other alternative to reducing the load on the contacts.

Frankly, cleaning the contacts can be done while still in the vehicle. The steering column housing still needs to be removed, and you just need to remove the switch from the column. Just be sure to disconnect your battery.

No problem with the bump! It's always good to have more discussion on topics like this.

One of the problems with cleaning the contacts is that often the surface is left rough which will tarnish more quickly than a nicely polished surface. If you are going to clean them, I would put a dab of dielectric grease on each of them to give some additional protection.

As far as a relay setup, it wouldn't be too terribly difficult. You really only have to do those contacts that have high current draw going through them. You would need to meet or exceed the amperage of the fuse for each of the inputs to ensure safe, reliable operation on each of the outputs. I believe that this could be accomplished with 3 50A relays on IGN0, IGN1, & IGN3. You could add another for the ACC output and a 30A relay for CRANK output which would capture all of the contacts that are used in these switches. That would create a low amperage connection at the switch saving the contacts.

One thing that this wouldn't address though is the issue of the passlock sensor going bad which is almost as prevalent as the contacts going bad.

Where is this Ignition Switch located, anyways? I have a '98 Blazer, my Repair Manual stinks!!! It often uses different names and terminology, for things, than are normally used by people in real life.
I had replaced the Electric Coil ($44), Ignition Control Module ($83), and the Starter Motor & Solenoid ($124), in February 2011. I did all this to get the dang thing to start and run. This may have been when I had Codes P0780 and P1860 come up before, but I'm not sure right now, still reviewing my Notes and Maintenance File.
OK.. I found a Note, that says 12/7/10 Service Engine Soon Light came on. Codes P0740 and P1860. So it could have taken 2 months for blazer to NOT start and run, before I did anything to fix it.
New FREE Fuel Pump was put in on 1/30/11.
New Sears Diehard Battery on 7/19/09, so it is 2 years & 2 months old.
Had had trouble with 4WD, but y'all helped with that. I took out the 4WD Module for awhile, then put it back in. Then the 4WD worked fine all Winter. That was on 12/19/10.

I KNOW I've seen a how-to for removing and installing the switch but I can't seem to find it this morning. Does anyone know where to find or feel helpful enough to post a link here? Thanks a ton! I've got a switch on order for this afternoon and want to remove the old one to get a head start on the operation.

Thanks in advance!

Found the How-To Install Ignition Switch forum:

https://blazerforum.com/forum/articl...-thread-26553/

So what is the part that I need to buy in order to fix the problem? I replaced the Ignition Lock Cylinder, but I am still having then issue of the dash lights and fuel pump not coming on all the time when I turn the key. The starter works every time no problem though.

Ignition switch is what you need to purchase...

Durlast LS1076 is the only one Autozone carries.

But don't throw out the old one. Keep it. You can gently clean all the contacts and put the old switch in a drawer for future use. When the new one starts to do the same thing, put the old one back in. Works for me anyway.

http://contentinfo.autozone.com/znet...S1076/image/4/

I've also had the 0300 code recently on my 2001 Jimmy SLE with rough idle and engine shutting down. Started as a blip here and there now it's not drivable due to shutting down and running like crap. Along with that I can't find whats poppong my IGN "E" fuse under the hood at start up.

Done the normal stuff. Dist cap, button egr valve etc. Getting ready to replace the coil and ign module.

Any one think that the fuse blowing and the shutting down could be related to the ign switch?

PS. Anyone have a good source for wiring diagrams or prints?

I have been working on a circuit design to integrate a marine grade, 120A, normally open, heavy duty relay to bypass the IGN 1 contact. These marine grade, high current relays have threaded studs on the high current side and are a steal at $10-$15 bucks apiece. When I get my mods done and complete my split charging circuit for my trailer, I will upload everything, but it will take me a bit of time yet.

Someone have a wiring schematic for ignition switch?
 

Bought a 04 LS 2dr, 2wd blazer from my boss that wasn't running,... Went from no spark, good fuel to good spark no fuel, I now have no power to the fuel pump unless I jumper the 30 to 87 terminals in the underhood fusebox..I know it will be the ignition switch but does any one have a wiring schematic for the ignition switch to the underhood fusebox? Please?

This is crazy, right? Or go to the repair shop and ask them to help

96 Tahoe ignition
 

Newby on this forum. Not sure if my reply is in right spot. Trying to take what you compiled here and apply to my ignition problem on 96 Tahoe 2 door. I see some differences. The B1 has no wire. I am needing to identify and test just one aspect of the circuit. Have no communication of 12V to these 3: IGN E, ECM 1, ENG 1.

I want to compare Pink thick wire to Red thick wire. However, I am testing a WVE brand replacement that has some issue I believe, and it has only been in a short time. I don't have a Pink thick wire. I have a thin pink but it is on the A row. On the B, in row 3, I have yellow (starter) and RED, supply 12 V next to it. Am I getting close on at least the red wire? We need to see the switching working on the ohm meter. Or this switch is killing my voltage to engine fuse panel.

The purpose of this thread is to discuss the content of the tech article in the original post which is specific to the 98+ s-series trucks and no others. As such, there isn't much to discuss here as you are talking about a completely different vehicle.

If you need help with your '96 Tahoe, please start a new thread in the appropriate section which sort of loosely fits into the Full Size K5 (1969-1991) GMT415 (1992-1994) Tech section.