Old TCS Wiring?

[spenceman72]

After researching this a bit, it that my 72 Blazer (4 speed manual, 4x4, HEI, elec. choke) was wired for this as the pictures show.
4 wires coming out of the firewall (thick red, black, blue, brown/wt stripe), all going across to the passenger side. The red wire went nowhere..was just dangling loose behind the motor. The blue and brown/wt stripe wire went into a connecter and was joined with a green/wt stripe wire that was connected behind the block on the passenger side but went no where. The black wire went behind the engine and is connected to the top of the transmission, right by the 2 wires which I believe are for the back up lights.
Everything seems to be running fine and I'd like to just remove these wires to clean things up, but 2 of them are actually connected. The black wire to the top of the transmission, and then the brown/wt stripe wire about 6 inches where it comes out of the firewall has a connection to a black wire, that runs back into the firewall. Now-since this brown/wt stripe wire wasn't connected to anything but that connecter on the passenger side, perhaps I can remove this? Hopefully my pictures below help..

[spenceman72]

Any thoughts? After some further research, it seems the black wire running to the top of my tranny (sm465) is the Reverse Light Switch? And the 2 green lights running to the top of the Tranny I believe are for back up lights? I'm not sure if I understand the difference between the Reverse Light Switch and Backup Light Switch though?
So, if I'm correct about the black wire being the Reverse Light Switch..I'm assuming I have to keep this? That leaves the brown wire/wt stripe that is connected to the black wire..still not sure what this is?

[spenceman72]

bump

[88Ironduke]

The connector pictured I believe went to a temperature switch. I had thought the TCS circuit also had a switch on the transmission that engaged when in high gear. Your reverse lights should come from a switch on the column in the cab. The black wire should be a ground for the relay can that used to be attached to the firewall around drivers side I believe. Hopefully the electrical gods can chime in because in my all of 72' schematic the TCS is not illustrated. In my case, I removed all of that stuff.

Paul

[VetteVet]

Here is a picture of a TCS relay with the same wires you have in your harness.
I'm guessing that the black wire from your reverse light switch on the trans is the one going to the relay in my picture and I think it is one of two going to the coil in the relay that closes the connection in the relay to power the vacuum solenoid on the intake manifold, which drops the vacuum advance portion of the distributor timing. This retards the timing for emissions control or so they thought when they designed this crap.I doubt that you have two switches for reverse.

There are several threads on the forum about this subject. Just type transmission controlled spark in the box by your PMs and tick the small circle by 67 to 72 chevy trucks click on google and it will take you to them.




The relay just above the TCS relay is the horn relay.

There are other relays on the firewall on some trucks that are part of this harness but it sounds like yours is inside the cab.

[spenceman72]

Thanks guys! I did the search, found this post,http://67-72chevytrucks.com/vboard/s...ad.php?t=53211, and have my answer.
The black wire plugged into the top of the tranny is indeed related to the TCS, a 'high gear switch' it seems. So-seems that I don't have to worry about that and can remove. This leaves me with the brown wire/white stripe that comes out of the firewall, and then is spliced into a black wire with a connector thing that then runs back into the cab. Not sure what this wire is?