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Old 08-09-2009, 08:53 PM
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Default 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 () and the thing popped apart like an antique clock, springs flying all over the place. 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:



C211 Connector Views:


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) circuit has power in OFF, RUN, and START
  • CRANK (small yellow wire) circuit only has power in START
  • ACC/RAP (large brown wire) circuit has power in ACC and RUN
  • IGN 1 (large pink wire) circuit has power in RUN and START
  • IGN 3 (large orange wire) circuit has power in RUN only
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.


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.

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.

/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!
Attached Thumbnails
Anatomy of the Ignition Switch-connectorc211_1of3.gif   Anatomy of the Ignition Switch-connectorc211_2of3.gif   Anatomy of the Ignition Switch-connectorc211_3of3.gif   Anatomy of the Ignition Switch-ign_switch_sch1of2.gif   Anatomy of the Ignition Switch-ign_switch_sch2of2.gif  

Anatomy of the Ignition Switch-ignition_switch_01.jpg   Anatomy of the Ignition Switch-ignition_switch_03.jpg   Anatomy of the Ignition Switch-ignition_switch_04.jpg   Anatomy of the Ignition Switch-ignition_switch_02.jpg  
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Old 08-11-2009, 04:32 AM
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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...)
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Old 08-11-2009, 07:22 AM
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Remove the two screws in the picture below (from your album):


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.
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Old 08-11-2009, 09:57 AM
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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...)
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Old 08-11-2009, 11:00 AM
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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.
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Old 08-12-2009, 08:03 PM
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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?
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Old 08-12-2009, 08:55 PM
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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..
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Old 08-14-2009, 09:43 PM
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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..
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Old 08-15-2009, 07:42 AM
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Definitely sounds like the ignition lock cylinder is worn out, not like an ignition switch problem.
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Old 10-04-2009, 11:44 AM
 
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Default 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
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98, 99, acc, blazer, cylinder, gm, ignition, ignitions, power, remove, retained, run, start, switch, wiring, work

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