Mystery wiring harness

[70 cst]

Wondering if any of you guys know what this harness goes to? It looks original to the truck but I can't find anything that it fits. Truck is a 72 custom 10 without air and a 307 v8 and 350 turbo transmission. The 2nd pic shows it coming into the cab and plugs into a relay. The 3rd pic shows the plugins.

[Jcfcamaro]

Looks like A/C connections

[VetteVet]

...............

Originally Posted by 70 cst

Wondering if any of you guys know what this harness goes to? It looks original to the truck but I can't find anything that it fits. Truck is a 72 custom 10 without air and a 307 v8 and 350 turbo transmission. The 2nd pic shows it coming into the cab and plugs into a relay. The 3rd pic shows the plugins.

Here's another picture and it's the harness for the TCS wiring. This was a pitiful attempt from GM to respond to the emissions mandate that the EPA forced on the manufacturers in the early 70s. It's called "transmission controlled spark" and
there is plenty of info on the forums about it, also google has lots of information.

Most of the owners of our trucks have ripped it out since the engines run better without it.



Some of the relays were mounted on the engine side firewall.



You don't have AC but the AC relay was mounted in the airbox if I recall correctly. That would be the only other stock installed harness.

[Ironangel]

VetteVet is correct (not that he needs me to back him up) "just sayin"

[GASoline71]

I have a 1972 GMC that had the "Spark Knock" wiring as well. I removed it all without any problems.

Gary

[Grandpas 72]

That wiring harness is a transmission control spark harness. It plugs into the TCS vacuum solenoid.
I hope this helps.

....the green wire goes to the temp sensor under the exhaust manifold on the drivers side I believe.

[71CHEVYSHORTBED402]

Originally Posted by Grandpas 72

That wiring harness is a transmission control spark harness. It plugs into the TCS vacuum solenoid.
I hope this helps.

....the green wire goes to the temp sensor under the exhaust manifold on the drivers side I believe.

I had the TCS on my 71, located on the engine side firewall. One unit is a relay and the other is a delay.

Interesting you should mention the green wire. What I found was a dark green wire that had been cut, and to-date I haven't been able to ID it. At any rate, I give up, what's a temp. sensor under an exhaust manifold?

My truck also had a dark green wire that ran to the temp. sensor that fits into the head. But the wire came off the driver's side of the firewall block.

[70 cst]

Guys I really appreciate the responses. The original engine is gone along with the emissions equipment. I wanted to remove this harness if it didn't have a reason to stay but I didn't want to remove something I may need.. I will go ahead and remove it and put a plug in that hole.