Who’s crazy idea was this? (1995-1996 CC wiring diagram)

So I’m getting really close to completing my drivetrain rebuild on my ‘95 cclb. The donor truck was a 2000 GMT400 reg. cab. Because of this I’ve found myself trying to merge the ‘95 interior cab wiring with the ‘00 instrument cluster wiring. Needless to say, I’m struggling. I think at this point I need to have sitting in front of me the wiring diagram for the ‘95 right next to the ‘96-00 wiring diagram. Can anyone help me out here?




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See if a wiring manual you need is downloadable in this thread.

https://www.gmt400.com/threads/88-95-service-manuals.43575/

Another option is alldatadiy.com, it would have the wiring diagrams. Cost would probably be around $50 for two VINs.


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I knew it had to be out there somewhere! Thank you so much!

Now I’ve got some reading to do. I’ll let you know if I ever get it figured out.

delta_p said:

See if a wiring manual you need is downloadable in this thread.

https://www.gmt400.com/threads/88-95-service-manuals.43575/

Click to expand...

So after staring at the wiring diagrams for hours now I’ve come to my options are not easy. This weekend, I got my hands on a ‘99 1500 suburban cab harness. It obviously has a lot more wires than I need. I’m thinking I’m going to have remove the entire ‘95 wiring harness, take it all apart, and rebuild it as a ‘96+ harness using all three harnesses. Before I dive into this I thought I might just ask if anyone happens to have a cab harness out of a ‘96+ crew cab with power windows and locks and without air bags.

I know it’s a long shot but it doesn’t hurt to ask.


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Update: So the majority of my issue boiled down to the ground wire for the power windows/locks/mirror moved after '95. Instead of coming from the instrument panel ground the moved it over to the new cab ground over by the HVAC box. By the way, someone at GM got lazy and never updated the convienence center pin callout in the manual. Either that or they changed it in ‘00 (I’m using a ‘98 manual, which I doubt since they switched all their engineering resources to the new trucks by ‘98).

They also moved the electrochroamatic mirror and cab clearance lights to their own connector where they were previously powered from the convenience center. I think they did this because they added a wire to the mirror to be able to turn off the auto dimming when in reverse gear. I moved everything back to the way it was in the ‘98 manual and just omitted the reverse wire since I’m using the ‘95 mirror.

I still missed something though because the courtesy lights won’t come on with the door switch. They will come on with override however. There’s also something up with the horn because it’s alway on, but that could be something I messed up when I reinstalled the steering wheel.

Finally, and worst of all, I have no spark at the plugs and I’m unable to communicate with the ECU when I plug my laptop into it. I don’t think this latest problem is a ‘95 to ‘00 problem because I didn’t touch any wires in the data link/ECU side of things and the parts truck that I took everything from was a running truck. At this point, the only ‘95 wiring left in the truck is the cab crossover harness and the front to rear chassis harness. Just to be sure I’ll trace the data link wires back to the ECU tonight, but I’m wondering if I somehow killed the ECU? I did check that there’s power to the ECU at the fuse panel in the engine compartment.

Does anyone know if the ECU holds back on both spark and fuel until oil pressure is detected when cranking? Or is it just fuel?

Did you rewire the ALDL connector too? The 95 has a 16 pin OBD1 the later models have a 16 pin OBDII - just a thought...

I transferred everything over from the ‘00 truck so that included the newer OBDII ALDL .


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Update:

It's alive! Meaning if started and ran. I only tested it for a few seconds. Next is to add antifreeze and power steering fluid. I just wanted to hear it run enough to say it's worth putting the rest of the fluids in and didn't screw anything else up. I sorted out horn issue. I inadvertently was sending the wire that was added in 96+ as part of the remote locks that makes the horn beep when you lock the doors to ground. I bypassed that and it's working correctly. I still have the courtesy light issue to resolve and the radio has no illumination, but does turn on. I'm not sure what my issue was with the no spark thing. It could have been I didn't have my test light hooked up correctly or didn't crank long enough. When I tried again later, I put the test light on the coil wire and got lots of spark! The main reason that it wouldn't start was that I had the distributor in 180 degrees off. [emoji849]

I've run it long enough to tell that it's missing and also sounded a little odd (tough to explain with words). Hopefully the missing is just a timing thing and the odd sound is just the power steering pump? I still can't get my laptop to communicate with the PCM! I'm going to try getting a different code reader tomorrow to try instead.

Things I've checked:

- Swapped PCMs with one from a previously running truck (same unable to communicate)
- 12V on Pin 16
- Continuity from Pin 2 to PCM connector
- Ground on Pin 4 (no resistance)
- Ground on Pin 5 (no resistance)
- Pins don't seem pushed back in the truck ALDL connector
- Pins are good and straight in my ALDL cable
- Verified my laptop can connect to another vehicle (2008 Saturn)

I'm assuming all the OBDII connection is looking for is the pin 2 communication wire, ground and maybe 12V? I don't think I've checked pin 5 ground, but if it didn't have a ground I wouldn't think the truck would run. Can the truck actually run but not communicate via the ALDL, some kind of internal failure? I've heard that if one of the sensors in shorted it can cause it to be unable to communicate. Any truth in that?

Any advice on this issue would be greatly appreciated.

Found good info here:

https://mechanics.stackexchange.com...anner-refuses-to-communicate-with-the-vehicle

Got it to communicate. I read somewhere on some forum, I can't remember now that someone that had a similar problem got theirs to communicate when they disconnected the ABS unit. I disconnected the ABS unit and low and behold, it now communicates!

No codes.

Does this mean this is yet another thing that is different from a ‘95 to a ‘96+? I thought the ABS units were the same. It was a fully functioning unit last I drive the truck. Maybe I damaged it in some wiring debacle? I guess time will tell.