Extra wire in starter loom

[79ramp]

I got my hands on a '76 C10 with a pretty fresh 454 and I am almost finished with a motor swap in my ramp truck (the old motor was running about 5 lbs cold start oil pressure (or less) before I pulled it ).

One thing I noticed while I was doing the swap: there is an extra wire which runs in the same 'loom' as my starter wiring. It appears to go towards the rear of the truck but it had been disconnected long before I got the truck. From what I can tell tracing it, it comes from the fuse box. Does anyone know what this is supposed to be connected to? IIRC, at one point I tested the wire and it is powered...can't remember if constant or keyed.

On the '76, the wire appears to go to the fuel tank, sending unit maybe? But if that is the case, I don't know why it would be powered.

 

[DanMcG]

What color is it?

 

[79ramp]

What color is it?

Whoops, meant to mention that. It appears to be orange.

 

[chengny]

Whoops, meant to mention that. It appears to be orange.

You noticed this wire in both the donor (76) and the recipient trucks? And in both cases it was run down to the area of the starter - but after it exited the loom, it headed back towards the rear of the truck?

On the 76, could the lead - that appears to go to the gas tank - possibly be tan rather than orange? If so that would make sense. On a 76 the sensing leg for the gas gauge doesn't run rearward with the rear lighting harness. It transits the firewall at the main bulkhead connector and then heads over to the RH side before heading aft towards the sender (the schematics don't show how it is routed over to the RH side, but it could very well be the case that it is run within the loom leading to the solenoid).

On the 79, there is an orange lead that goes rearward (if equipped with a TH400 transmission) - it supplies power to the detent (kickdown) solenoid. But in my experience it has it's own grommet where it transits the firewall. But the grommet is on the LH side of the FW and the wire runs down the LH side of the transmission. Also - unless the kickdown switch (mounted to the gas pedal bracket) is stuck closed - it should not be hot. It should only be hot if the accelerator is almost to the floor.

The gas gauge sender lead on a 79 is pink and is run aft in the same loom as the rear lighting harness.

 

[79ramp]

You noticed this wire in both the donor (76) and the recipient trucks? And in both cases it was run down to the area of the starter - but after it exited the loom, it headed back towards the rear of the truck?

On the 76, could the lead - that appears to go to the gas tank - possibly be tan rather than orange? If so that would make sense. On a 76 the sensing leg for the gas gauge doesn't run rearward with the rear lighting harness. It transits the firewall at the main bulkhead connector and then heads over to the RH side before heading aft towards the sender (the schematics don't show how it is routed over to the RH side, but it could very well be the case that it is run within the loom leading to the solenoid).

On the 79, there is an orange lead that goes rearward (if equipped with a TH400 transmission) - it supplies power to the detent (kickdown) solenoid. But in my experience it has it's own grommet where it transits the firewall. But the grommet is on the LH side of the FW and the wire runs down the LH side of the transmission. Also - unless the kickdown switch (mounted to the gas pedal bracket) is stuck closed - it should not be hot. It should only be hot if the accelerator is almost to the floor.

The gas gauge sender lead on a 79 is pink and is run aft in the same loom as the rear lighting harness.

Well, I noticed a wire on both trucks...not necessarily the same wire. However, in both cases it appeared to run the same from the starter loom (I did not yet trace the wire back to its origin on the '76) so I thought there might be a connection. I expect you are probably correct on the '76.

As for the '79, the orange wire for the kickdown is in a separate location and I already hooked it up so I know that is not it. I have not looked for the sending unit wire on the '79 but will crawl under there and check, imagine it will be with the lighting harness.

The '79 has had a fair amount of shoddy "custom" electrical work (for instance, the dual battery wiring consisted of the end of one positive cable twisted around a bare section on the other and wrapped in electrical tape ). I'm going to guess that this was another addition by the PO. Going to see if I can get a continuity tester and at least check which fuse it goes through.