unused wires?????

[Jarhead79]

Had a nest of wires in my 79 gmc behind my master cylinder that have been bugging me since this time last year. There is a dark green wire, brown wire and tan/pink/salmon color wire coming out of the firewall that doesn't go anywhere. I have no clue what they go to but I have an idea that it's my temp gauge and oil pressure gauge in my dash since those don't work. Maybe? I posted the other day about wiring up other gauges and have those working but instead of getting rid of the wires by cutting them out right now I'm wondering what they are first or if I'm guessing right. Then there is one more wire that is by itself coming out of the fire wall to the left of the other three wires. Not sure what it went to at one time either.

 

[74 Shortbed]

Looks like the spaghetti pile that was in my truck when I took it all apart, and under the dash was a total nightmare, lol..

 

[Jarhead79]

I think I figured out the single orange wire is for the oil sending unit! Which I don't have since my aftermarket gauge is connected there with a copper line.

 

[74 Shortbed]

Well, that's one wire out of the way, wild guess green is water temp????..

 

[chengny]

The ORN wire is almost certainly the power from the kickdown switch on the gas pedal to the detent solenoid on the transmission.

DK GRN is gauge sensing leg to coolant temp sensor (front LH cylinder head)

TAN is gauge sensing leg to oil pressure sender

The PNK lead is the hot wire from the ignition switch to the coil - I don't know how you're running. It is also branched off for power to the speed switch and speed switch solenoid.

If that separate wiring group is any indiaction, you must have a Mark V8:

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[Jarhead79]

The ORN wire is almost certainly the power from the kickdown switch on the gas pedal to the detent solenoid on the transmission.

Hmmm I stand corrected then, but it has me baffled now because it wasn't hooked to anything and my truck goes into passing gear when I tromp on it.
I do know the wiring on this truck has been hacked and changed. I really would like to redo it but so far everything works as it should. Just not sure how things are really wires up, I even have a grounding strap that's not connected from motor to cab, but noticed last night there's a ground wire from the core support to the frame near the batery. My a/c compressor is connected to a green wire that comes across the firwall from the passenger side. Lol hate it when people Jerry rig things.

 

[HotRodPC]

Make sure on the ORN wire. Your truck didn't come with a Th400, so it may not be for the kickdown solenoid. Though it's possible all the automatic trucks had that wire regardless of the transmission. Manual Trans trucks would have had Clutch Switch wires.

 

[Jarhead79]

I've gota th350

 

[HotRodPC]

I'm aware, so you don't use that orange wire for kickdown solenoid if your truck is equipped with that wire for that purpose. I'm thinking No because I'm fairly certain the Th400 kickdown solenoid wiring harness is stand alone. Seems I installed in a truck we converterd from Th350 and installed the switch and all just like OEM.

 

[Jarhead79]

Cool beans, I can clip it and dispose of it! Lol may go ahead and get rid of the other wires also since I'm using other gauges, eventually I'm going to just put in all new gauges, just wanting to get rid of the useless wires. Am really wanting to shorten some wiring up a bit. It seems I have about 6 inches of excess wiring that just is an eye sore. Trying to clean it up some. Eventually I'm gonna swap my motor with another one I'm building and want to cleanup the firewall and get it painted a solid color, was white, but some one half added spray bombed it.

 

[chengny]

Sorry about the misinformation on the orange wire .

Before offering that suggestion, I looked at your vehicle profile - but I couldn't find any mention of what model transmission you have installed. I always see the orange wire for the detent solenoid (TH400) coming through the firewall at that particular grommet so I assumed it was that. To be sure, I checked the 1979 wiring diagrams. They show a "transmission kickdown solenoid" in the engine compartment and a "transmission kickdown switch" in the cab connected by a dotted line line labeled "orange".

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Wiring shown as a dotted line - rather than a solid line - indicates that the connected components(s) was available as an option. Knowing that the TH400 is GM's only transmission with an electrically operated solenoid - I took a chance. But not knowing for sure where the wire goes to after penetrating the firewall, I used the phrase "almost certainly".

If it doesn't go to the transmission, where it does go. I would be interested in finding out. Did you try to follow it back but it gets hidden and can't be traced?

 

[HotRodPC]

I didn't look at it cuz I don't see those well, but I have a feeling according to the diagram you were right Jerry. Many of these diagrams are generic and our trucks are NOT a one size fits all when it comes to wires. This is why I like the Actual GM OEM wiring books. But by the time you scan and post they're so small they're hard to read and follow.

 

[chengny]

I didn't look at it cuz I don't see those well, but I have a feeling according to the diagram you were right Jerry. Many of these diagrams are generic and our trucks are NOT a one size fits all when it comes to wires. This is why I like the Actual GM OEM wiring books. But by the time you scan and post they're so small they're hard to read and follow.

No, no - I wasn't asking why you couldn't trace the wires. I was wondering why Jarhead79 was unable to follow the leads to their termination and just see what they were connected to. Maybe I'm not reading things right and these wires have all been cut - that would make tracing them impossible.

 

[Jarhead79]

They were all cut and just in a spaghetti ball behind the master cylinder, I just wanted to clean things up a bit but kind of wondered why they weren't being used, it was bolted to the firewall just above the drivers side head but didn't go anywhere.