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72Thunder 01-18-2015 10:54 PM

Under Dash Relay??
1 Attachment(s)
Hi all,

I have recently begun stripping the interior of my 1972 C10 and came across this relay under the dash above the fuse block, but to the left of the horn relay. It has a brown, blue, black and a possible 10ga. red wire (this one isnt hooked up) connected to the relay and all taped together that comes out of the driver's side of the firewall. Could anybody tell me what this relay is used for and what the wires are indicated as?

Thank you very much in advance!

72Thunder 01-18-2015 10:55 PM

Re: Under Dash Relay??
Sorry for the mess of wires. The relay is circled in yellow!

VetteVet 01-19-2015 12:35 AM

Re: Under Dash Relay??
1 Attachment(s)
That is probably the TCS relay. An emissions rely that the factory used to comply with EPA regs in the early days to control emissions by retarding the ignition timing . It stands for transmission controlled spark.

Here is another view.

Attachment 1351456

72Thunder 01-19-2015 01:51 AM

Re: Under Dash Relay??
Awesome, thanks for the information! Would that be a "should have" or "need to have" when I switch out my TH350 to a 700R4 or just throw it in the trash? Like I say, it looks like all the wires were cut about a foot and a half out of the firewall.

VetteVet 01-19-2015 09:10 AM

Re: Under Dash Relay??
You won't need any of that stuff for the transmission. There may be a vacuum switch on the manifold and a switch on the stock transmission. There may be some wires and a relay on the firewall depending on what the original owner removed.

Here is a group of threads for some more information on the system.


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