The Stovebolt Site Forums The Shop Area The Electrical Bay 1970 GMC 1/2 ton wiring mystery

Ok, I'm starting my latest project. It has a 307, 3 speed on the tree. I haven't been able to locate a schematic that addresses this item. Previous owner(s) have cobbled up some wiring over the years and left some dangling. Specifically I'm looking at what appears to be a second temp. sensor in the the right hand head with a green wire that goes to a relay on the firewall. The relay has a pink wire that goes to an always hot terminal on the fuse panel. There is a blue wire on it also. I also have black wire coming out of the trasnsmission, not plugged into it, literally goes in through a hole in the transmission and I can push and pull it about. ???? In my searches I'm finding similar schematics that show a transmission relay switch and a second temp switch with a time delay relay all being used for spark control???

I sort of remember that system, and your research is correct- - - -it was a very early emission control system which only allowed the vacuum advance to operate at certain engine temp and gear selection situations. I'd suggest simply disabling the whole works- - - -it was pretty much a bust, and it made the already puny 307's performance and gas mileage suck even worse!

I was running a shop in California in the late 1970's, and it was a constant hassle to keep up with all the exhaust emission regulations. Back then, cars in commiefornia had to pass an annual emission control inspection before license plates were issued. Getting that "state inspection station" license involved making some under the table bribes to the state "clean air" people, but the shop owners who got the license got rich on the inspection fees! (No, my shop didn't qualify!)
Jerry