While the engine is out of my '70, I started cleaning up the wiring harness. The Alt external V-reg wiring has been changed to internal V-reg and the yellow/white coil wire has been replaced with a 14ga wire for the HEI. I came up with some extra wiring that has me puzzled.

The red lead in wire comes from the fuse block and is hot with the key on. This wire comes through the fire wall all by itself, but it is factory installed. The red wire goes directly to a block on the passenger side firewall just above where the tranny dip stick should be. From the block comes a blue and a green wire. The green wire goes to the temp light switch on the pass side of the engine. The blue wire goes to a two wire connector the used to go to a vacuum switch mounted by the carb. The second wire from the vaccum switch connector goes to a single wire connector on the tranny.

So, what is the block on the fire wall ,the vacuum switch, and the tranny switch for? The vacuum switch has been disconnected for years. I thought it might be for the backup lights, but that should have a two wire switch. This does not. I want to remove any extra wiring to clean up the engine bay. By the way, I have removed all the wire wrap to verify the wiring connections.

I have pictures, but I do not have them posted on any web site yet.

Might be a TCS system (transmission-controlled spark). It cuts off vacuum advance except when the transmission is in high gear. It's a smog device.

my buddies 72 k5 has a factory "fuel efficency" guage that runs on vacume of some sort, i havent really taken a close look yet. maybe??????

Might be a TCS system (transmission-controlled spark). It cuts off vacuum advance except when the transmission is in high gear. It's a smog device.

Never heard of it before. Make sence though.

How about the block on the fire wall? I have not ohmed it out yet. It is kind of big just for a distribution block.

Okay, let's try adding some pictures.

http://www.myoldtruck.com/gallery/files/1/6/6/4/Firewallconnector2.JPG

http://www.myoldtruck.com/gallery/files/1/6/6/4/Vacuumswitchconnector2.JPG

http://www.myoldtruck.com/gallery/files/1/6/6/4/Trannyandtemplight2.JPG

I did mistakenly say that the green wire goes to the temp light. It does not go to any light or gauge, but the wire does go to a sensor in the water jacket close to the motor mount.

And here is the vacumm switch. It does seem to divert the vacuum depending on the coild being powered or not.

http://myoldtruck.com/gallery/showimage.php?i=4276&c=3048
( Picture link failed! ??? It worked just a few minutes ago.

I can see how the tranny switch would open and close the vac switch and shut off or turn on the vacuum to the dizzy vac advance. BUT, what is the temp switch for?

Also, I ohmed out the firewall connector. There is a resistor from the red supply wire to the green wire and it looks like a resistor from the green wire to the blue wire.

I think I can just pull all of this "system" out and just use the red wire for my electric choke.

Temp sensor is part of the TCS. The piece on the firewall is a relay. It and all the associated wiring can be outed.

Great! That will leave me with a nice hook up for the electric choke. Thanks for the help.