1972 Super Cheyenne- Wiring Help

[BB72CAMARO]

I found these wires bundled together, taped up and not hooked to anything. They come into the engine bay through a grommet in the fire wall and look factory. Please help identify what they are supposed to be.

[demian5]

I have a bundle of wires tied to my firewall on my 70. I believe they were for any smog equipment but I'm not sure either...

[Bigdav160]

Transmission Controlled Spark

I eliminated mine entirely

[demian5]

Originally Posted by Bigdav160

Transmission Controlled Spark

Like when the shift linkage shorts out against the harness when you put it in reverse - but only on an incline where the rear of the truck points down?

[BB72CAMARO]

Can you identify the wires by color? I assume the pink is fused ignition hot.

Not sure about the blue, black and gray/white wire.

Also, the gray/white wire insulation is melted.

[jocko]

I don’t have it handy - but if you google hi res wiring diagram in the search box at the top right and click the 67-72 radio button, you may find what you need - but at the very least, you’ll have a free wiring diagram.

[BB72CAMARO]

Thank you sir. All the wiring diagrams I have found don’t include the transmission timing control.

[68 P.O.S.]

Yeah, looks like the TCS harness. I kept the power wire and used it for my electric choke

[BB72CAMARO]

Do the other three wires go to the control relay?

[68 P.O.S.]

I honestly don't recall, it's been a few years. I believe they do, but I can't say with any confidence. Anyone else here know for sure?

[jocko]

see pg 253 of Hatzie's 72 service manual (72: 330 72 ... etc) - it MAY help,. but not a quick answer as to wire colors.
http://67-72chevytrucks.com/vboard/s...d.php?t=558016

[Ironangel]

Big Dave is correct, they are/were the wiring for the Transmission Controlled Spark system. They do not appear in the standard wiring diagrams for some unknown reason? The 10ga. pink wire is an excellent switched 12 volt source for HEI systems or electric chokes. They are explained in detail in the 72 truck shop manual, heres a brief outline from Autozone, https://www.autozone.com/repairguide...00c15280080d56

[Steeveedee]

You can remove the relay and the wiring if you want, and use the power wire as has been stated. TCS was used to inhibit vacuum advance until the vehicle was both at operating temperature and in high gear (it was used on both automatic and manual transmission equipped vehicles). Limiting vacuum advance was an early version of an oxides of nitrogen reduction SMOG control. I think that it went away with the advent of the EGR system, which was also used to reduce peak combustion temperatures in the effort to reduce oxides of nitrogen. I was a mechanic back in those days, with a SMOG license. Elimination of the TCS system with the advent of the EGR system may not be correct, on my part. I'd have to go look it up; that part of my memory is failing me at the moment.

If you have a thermostat housing with a thermal switch in it (might be gone by this day and age) that is what was used to allow vacuum at temperature. That housing may have been replaced since new with one that has no provision for the thermal switch.