Last year I put my 2000 4wd Jimmy in a ditch, and had a section of harness that ended up sitting on the y-pipe without me knowing, which caused a fire the following day. I'm finally getting around to repairing it now, and could use a bit of help.

I cut out the burnt section, and am replacing it with wiring from my 99 4wd Blazer parts truck. I got some of the obvious matching wires connected, but due to discoloration from age and grease, and me being partially colorblind, I'm having issues with the rest.

The section of harness that I'm replacing runs to the PNP switch, which has 11 pins across 2 connectors, and to the B1S1 O2 which has 4 pins, for a total of 15 pins. Problem is, there are 20 wires in the harness. I don't know if some of them end up connected together inside the loom somewhere, or what.

I've traced the pin out for the 4 wire PNP plug to the C3 connector at the VCM, and traced the the O2 sensor wires to the C1 VCM connector, but cannot trace the 7 pin PNP plug, with the exception of 1 ground wire. I don't even see it listed in any schematics, other than that one wire.

I plan on testing for continuity from the pins in new plugs, and labeling the wires, and testing for continuity to the wires in the original part of the harness in order to match everything up, but I don't know what connectors to probe to know what wire is what.

I've tracked down what the wires on the 7 pin connector are for, and they are as follows

Pin A----ORN/BLK----Circuit 1786----From What I can find there is actually no wire here???
Pin B----LT GRN------Circuit 275------Shift interlock (not required???)
Pin C----PNK-----------Circuit 839------Switched 12v
Pin D----BLK/WHT----Circuit 451------Ground
Pin E----PPL/WHT----Circuit 1035----12v Ign in start position
Pin F----LT GRN-------Circuit 24-------To reverse lights
Pin G----YEL------------Circuit 1737---To starter motor relay

That's as far as I've been able to get with that plug, and cannot figure out which connector(s) to probe in order to test and match them to the new section of harness.

If worse comes to worse, I can always bypass the original section of the harness, and run a 12v switched wire for pin C, ground for pin D, 12v start wire for pin E, reverse light wire for pin F, and starter relay wire for pin G, but I don't know what to do with pins A and B, and I'd rather go through the harness if possible.

 

Anyone?

I've been combing through schematics for a few days now, and have not been able to fine any info for this plug or it's wires, other than I may be able to test the wires for continuity to the B/U fuse for the wire that goes to pin C, and maybe at the BTSI fuse for the wire that goes to pin F.

Don't know if that would work though without the battery installed, and the rest of the switch wiring being hooked up.

 

I was going to offer to look in my schematics in my 99 service manual. Is that what you have? Or are your schematics for a 2000? Maybe they are slightly different?

 

Truck is a 2000. My schematics are for a 99, but are missing a few diagrams. I pulled up a full diagram for a 2000 online, but still couldn't find this connector.

It's the Park/Neutral Position/Back Up switch. Every diagram so far shows the part, but only shows the wiring for the PNP connector, but not the Back Up connector.

It looks like circuit 839 (pin C) possibly runs to the B/U fuse, and that circuit 24 (pin F) may run to the BTSI fuse. Circuit 451 (pin D) is easy enough, as it's just a ground. The rest, no clue.

 

Been combing through schematics for a few days now to figure out where to test the original side of the harness for continuity, in order to match the wiring up to the new section. None of them show this connector, but I may have made a little progress.

Pin A-------Not used
Pin B-------Shift Interlock-------------------Not sure, but could just save it for last.
Pin C-------12v Switched-------------------Test from B/U LP Fuse?
Pin D-------Ground---------------------------Should be easy enough to just test each wire for continuity to ground.
Pin E-------12v Ign in start position------Test at pin 85 of starter relay?
Pin F-------To reverse lights---------------Test at BTSI fuse?
Pin G-------Park/Neutral Signal----------Test at pin 86 starter relay?

Other than those wires, I just have the power and ground wires for the o2 to trace and connect, and 3 wires that I've already confirmed on the original harness side, but have no continuity to the plug on the replacement side, so I'll need to run ones, but that's not a big deal. It's really just this plug that for some reason is left out of every schematic I can find that's holding everything up.

 

Took a few minutes today on my way home to stop and go through some more wiring. Most everything is traced, labeled, and connected. With the exception of a few wires.

I've got no continuity from :
The 4 wire NSS/PNP connector Pin B-----Runs to Trans range Signal C
The 7 wire NSS/PNP connector Pin G-----Runs to Park/Neutral Signal
The VCM C3 connector Pin 26--------------Runs to Trans Range Signal P
The Chassis to Body connector Pin A-----Runs to VCM C2 Pin 2

This is before any connections have been made for these circuits. Testing directly from the pins in the connectors to the ends of the wires. Very strange since the original wiring still in the truck was unaffected by the fire, and the section I'm using to replace it came from a truck that had no wiring issues. Although the parts truck has been just sitting in the back yard for 7-8 years now, and with all of these connectors unplugged for about 4-1/2 years.

I also still have to trace down the wires on the original side for:
The o2 sensors 12v switched wire, which is supposed to run to the oxygen fuse
The Shift Interlock /PNP Park Signal wire, which I was able to verify connects to the BTSI fuse
The Park/Neutral signal wire which should run to pin 86 of the starter relay.

Problem is, when I tested for continuity from the oxygen fuse, I have two wires that are the same size, and faded to the same color, that both show continuity to both terminals with no fuse inserted.

I think if I focus on the wires with no continuity 1st, and get that sorted, then I'll only be left with 3 sets left to connect.

On the plus side, I applied power to the battery cables and I have power in the truck.Interior lights, and dash lights/gauges all working.

I realized there's no suggestions or interaction here, but posting this helps me to keep track of what I've found, and done, and may help someone in the future.

Once I have everything traced and connected, and can verify that everything is working as it should, I'll post a complete breakdown of all 20 wires that run to these connectors, with what they are for, and where each wire terminates at each end. That way if anyone is ever dealing with issues with one or more of these circuits, they won't have to go though all the hassle of tracking every one of them down as I have.

 

I don't know about anyone else, but I'm invested in hearing of your progress. And as you say, this could be exactly what someone else might need someday!

 

Got the last of the wiring connected, other than the two ground rings at the back of the engine. I took two jumper wires, and ran one from the ground rings to the neg battery terminal, and another from the rings to the alternator case temporarily just to test things out.

I've got power. Dash lights, gauges, radio, running lights, brake lights, blinkers, all working, but when I turn the key to the start position I get nothing. No crank, and I can't shift out of park. Button will not press in. I know that generally that is an issue with the shift interlock, but I rechecked, and the correct pin from the Park Neutral Position switch is connected to the wire that had continuity to the BTSI fuse.

I know that the Park Neutral Position switch will need to be adjusted since the old one was burnt, and I swapped it out with one from my parts truck, so the next step, will be to adjust the switch the see if I can get it to crank, and hopefully start. Then if it still won't shift I will address the shift interlock circuit.

 

Adjusted the Park Neutral switch today, and still no crank. Jumped the starter relay, and the truck would start for maybe 1 second and die. I noticed that the cables were getting warm, so i disconnected the battery. Seems that there is either a short, which is the least likely scenario, or a wire hooked up backwards.

Only wire that I can think of that could be wrong is pin E of the 7 pin PNP plug, although it's possible that it could be a different wire considering how well GM completely hid any and all info on this plug in all of their schematics. I did however track down a pin out of the 3 main underhood fuse box connectors, along with where each pin runs to by circuit number, so I have remapped the wires based off of this. Only one pin from this plug is unaccounted for in the pin out, but I should be able to figure it out, so long as the other pins are correct.

My next step will be to cut the 6 wires going to the plug, retest continuity to the corresponding pins in the fuse box to label each of the 6 wires, reconnect them to the appropriate wires from the plug, and test again. May be a few days before I can get to it with everything going on right now, but I'm not ready to give up on this gal just yet.

 

Disconnected the wires from the 7 pin Park Neutral Position switch today, and tested each wire for continuity to the corresponding pins in the fuse box. Sure enough Pin E was wrong, and was not getting voltage to the switch, and therefore not passing the voltage through Pin F to the starter relay. Fixed the wires, and now the truck cranks off the key and the shifter unlocks as it should.

Only issue now is that I suddenly have no spark. Not sure what the reason is yet, since none of the wires I'm working on should have any effect on the coil.

After tracing the power from the coil circuit, the next step will be to test for power with key on, and while cranking at
the coil
the ICM
the ECM1 fuse
the VMC C4 connector pin 18
the crank sensor plug