Another "what's this wire?" thread

[Komet]

I'm working through what's left of my chopped harness, and I could use some help identifying what a couple wire clusters are for. 92 K2500 6 lug ECSB, I believe it's got the trailering package and was a factory dual battery truck, here's what's left of my rpos:

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The first is a black and brown pair, thin gauge, and it comes out of its own grommet on the driver's side firewall:

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Maybe aftermarket something and the grommetted hole was repurposed?

Next is a chopped set of red, tan, grey, green, and brown:

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These lead to the driver's side lower connector area. Maybe the original trailer harness stuff? Colors don't match though, unless they change to brown, yellow, dk green, light green somewhere. Maybe 4l60 stuff? Truck has some other mopar trans at the moment.

Any help would be appreciated!

 

[packer0440]

That first one is a little hard to see, but if it's one wire it kind of looks like the tachometer pigtail.

 

[Komet]

Ok so I traced out the BRN wire, and it's definitely going into GT105, although it's been depinned from its connector on the other side and connected to '39 BLU' in the fusebox (somebody must have changed this). The black paired wire goes to '150 BRN' where I would expect, because I'm pretty sure these would have gone to the Auxiliary Battery Relay based on the ends of the connectors, length of the connectors, and where they naturally want to bend up into.

 

[Komet]

More info on the other bundle:

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I get +12v in RUN for GRN, and I get +12v in RUN and START for RED and BRN. I get 8.5v on TAN in RUN and START (sensor?), and I get no real reading on GRY in any mode.

 

[GoToGuy]

Do you have the wire diagrams.? Did you say " Mopar" transmission?

 

[Komet]

Do you have the wire diagrams.? Did you say " Mopar" transmission?

I do, no luck finding that particular combo of wire colors going to one specific place so far. My best guesses for the 5 wire bundle are trailer wiring, 4x4 related stuff, or maybe fuel pump. Most likely I'll cap them all off or use them as 12v switched trigger sources as needed.

Yeah it's some Mopar thing that bolts to a 12v Cummins. Truck was a swapped project that has since been harvested for said Cummins and a few other bits, I am going to swap an L31 / 4L60e combo into it.

 

[GoToGuy]

If you have some butchered old project, it would probably save time in the long run remove the convoluted tubes then trace the wiring AND MARK the wires. Using the factory service manual.
It tells you where the wire looms are routed. Shows where the grounds are located. All the colors are identified, the splices. What connectors look like, even end views shape. If you think it's camper wiring or if it's trailer wiring. There are two trailer wiring options. You can identify what you have by the RPO label. Have decided the RPO codes yet? If you use the service manual for your year pickup the first chapter list all the option codes for that year, and the definitions for that year. A little easier than going through a " 0, zero" to " Z" listing the big one has a thousand codes? That's how I would attack this problem. The factory manual has so much good info, not complicated just very thorough and complete.
Good luck.

 

[Komet]

I've made some progress on this. I took the brute force method and searched the wiring manual for every reference of DK GRN, TAN, PNK, etc and came up with a list of things that could possibly connect to C100. This 1988 C100 pinout diagram was also helpful:

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Also, I made a mistake with RED. Turns out it's PNK, but dirty, which was a game changer because RED wasn't making a lot of sense. So I verified DK GRN is Coolant Temperature Gauge by grounding it briefly and watching the gauge move, and I also verified TAN is Engine Oil Pressure Gauge by doing the same thing.

BRN could very likely be the alternator excite wire, I haven't verified that yet but it makes enough sense given that it's +12v in RUN and START. PNK is throwing me for a bit of a loop. It's a thick wire, and it would certainly make sense that it's power to the coil. However, when I pull either/both the INJ A/B and ECM/IGN fuses, PNK still has +12v in RUN and I would expect it to lose +12v with both fuses pulled.

GRA might be something related to the fuel pump / oil pressure switch, not really sure. I suppose the next step is to remove the C100 and get an exact pin location of the remaining wires to really nail it down.