Oops, my mistake, yes ON meaning RUN position.

Fuel pump relay latching coil ground is good. (zero ohms)

Need to know, when you can, if the fuel pump relay is receiving a trigger signal from the PCM. (my guess is no) We know the fuel pump receives voltage through the blue jumper just in front of the relay. My guess is that the fuel pump runs continuously when the ignition is in RUN and START positions, (it shouldn't).

The blue wire going to the starter solenoid, (if that's where it goes) is a problem. Need to know exactly where it goes. Results may send us into the ignition switch to check some circuits there.

In the instrument cluster there is an indicator light that says "Security". It should come on during the bulb check and turn off, does it stay on while the engine is running?

EDIT: Check both sides of the CRANK fuse with the ignition in the START position, should show battery voltage.

 

A couple things I've noticed, since I can't work on it any more tonight. When I had all the jumper wires pulled off, I could hear the fuel pump when I went from RUN to OFF...??? It didn't always do that, but not when it was in RUN. I'll test it to see if it's getting a signal from the PCM on Thursday, but I'm out of town tomorrow night.

I just replaced the ignition switch the other day. It seemed, from reading the forums, that it could be my ignition switch, so I went ahead and replaced it. For whatever reason, it wouldn't even turn over without that blue wire on the CRANK wire. So I put it back.

The security light is on all the time when the ignition is any position except LOCK. The airbag light is also on all the time.

On the underhood fuse panel, the fuel pump relay is VERY loose. As in no resistance to put it in or take it out. Same with the headlight power relay. Could that be a contributing factor?

 

It's normal for the pump to run for 2 seconds after turning the ignition to the OFF position.

Something screwy with the blue wire, it might be bypassing the neutral safety switch. If that's the case, the starter will engage with the gear selector in any position.... danger!

Security light might be an issue, and the reason for all those jumper wires. It could be they were trying to bypass the Passlock system. The air bag light might be something all its own, we'll see. It's the least of the problems right now.

Fuel pump relay loose, yeah that's a problem. Might have to tighten up the terminals.

Somebody obviously knew what they were doing to a certain extent, but not enough to figure out the root cause.

 

I was planning on going down to the junkyard to pick up a few things for the truck this Friday--would getting a fuse panel be a good idea?

If it is some sort of Passlock bypass, how would we fix that?

I'll see about following that blue wire on Thursday evening as well to see if I can find where it goes.

 

Or am I getting ahead of myself?

 

We don't know what the problem is yet. That's the whole point of diagnosis, so money isn't spent needlessly.

 

In the instrument cluster: Does the "Service Engine Soon" indicator come on during the bulb check and then turn off when the engine is running?

Are there any Diagnostic trouble Codes, (DTC's) in memory?
If so, what are they and what order were they retrieved?

 

Sorry it took me so long to get back to this. I've been out of town for a few days for work.

I haven't had time to trace that mystery wire yet--planning on tomorrow for that. But I did find out that whatever has been done does bypass the park/neutral safety.

Also, ever since I put the jumpers back in (I have to get to work somehow), the truck now won't shut off when I turn off the ignition key. Any ideas on a quick fix for this?

To answer your questions, yes, the SES light comes on but goes off after the bulb check, and there aren't any DTCs in memory--at least none that the Autozone people could read.

I'll check the blue wire tomorrow. I'm going to have to cut a lot of electrical tape off to find where it goes--they didn't replace the wire protectors, just taped the whole thing. I can't see where it exits the bundle, so I'm guessing they spliced it in somewhere. I'll let you know.

 

Ok...

So I went out to go to the store and it wouldn't start. Which means something drained my battery overnight.

I did, however, manage to track down the blue wire. Unless I'm reading this schematic REALLY wrong, it's connected to the large purple wire that goes from pin 87 on the starter relay to the starter solenoid. So yes, it bypasses the starter relay, the PN switch, and the 10A crank fuse.

 

Wow, what a mess. It's not surprising the battery went dead with all the jumpers. Good job interpreting the schematic: if the blue wire runs from the yellow wire at the ignition switch to the purple wire between the relay and the starter, you are absolutely correct with the components that it bypasses. The question is why did they do it. This is not what caused the battery to go dead though. I suppose at this point, you might as well clean up messes as you find them. It appears in the image that they used what's called a "Scotch lock" connector. GM does not use them so whenever you come across something like this, or a crimp connector, somebody has been there making a mess.

To figure out why they ran the bypass wire....
At the starter relay:
The red wire should show battery voltage at all times.
The purple with white trace wire should show battery voltage with the ignition in the START position, and trans in neutral or park.
The black wire should show less than 5 ohms resistance to ground.
If you apply battery voltage to the purple wire, the starter should engage.