This one is in similar location to back up light switch. It is attached on transmission right behind clutch fork. It is cut about 12" from connection onto transmission housing.

 

For transmission controlled spark. You'll get better answers if you tell us what year you're working on.

 

Profile says 71, transmission controlled spark switch, part of the emissions system, you only get vacuum advance in 4th gear.

 

Thanks. Seems like it is no longer needed. Is there a clean way to eliminate it?

 

If it's no longer needed you should be able to trace it back to where the solenoid on the intake was originally located.

 

On a 1971 it provides vacuum to the distributor thru a relay on the firewall then the CEC carburetor solenoid is energized to port vacuum in 3rd and 4th gear. Not just 4th.

 

Thanks for the info on this. The engine, intake, carburetor, distributor, are all aftermarket.

1971 coupe
gm goodwrench engine w/ stoker kit 383ci
m20 trans
edelbrock victor jr intake
Brawler 680 carb

But now I'm wondering if the contining electrical issues I've been having since the engine was rebuilt last fall are related ....

The first time we fired it up after the new engine was installed, it blew out the MSD box. Eventually, I replacd the MSD with an HEI ignition control module. I've also replaced the coil and alternator. It has the correct voltages everywhere, and I haven't blown and ICM since the new alternator. I've driven in the car for 20+ hours total. Since the new alternator

The other day I noticed the transmission vacuum advance wire on the transmission that was cut off, and coiled it up to keep it out of the way. Drove the car to a cars and coffee this morning, then on the way home the car died again. I thought it was the ignition control module again, so I swapped it out for the spare one I've been carrying around. No joy. The engine turned over all and the electric was working, but the engine would not fire. Called a tow truck to bring me home.

Back in the driveway, I started checking voltages and found 0 voltage at the 12 volt wire to the coil and HEI module. Checked the fuse box and it turned out the fuse in the "radio tsc sol" slot was blown. The fuse says 32 v on it. I think its a 20 amp.

Fortunately, I had several spares, when I put it in, the car jumped like the starter kicked in for a moment. Stupid me I didn't disconnect the battery. And the new fuse was blown right away. So I hit the kill switch pulled out the new bad fuse put another one in. When I turned the kill switch back on, the car jumped again, but this time did not blow the fuse. And it started right up. But now I'm really confused. So it wasn't the ignition control module after all. I put the original one back in, and it worked fine. Is the ignition dependent on this fuse?. I'm not sure how these cars we're wired from the factory. When I bought the car, the MSD box had been wired, per the instructions, directly to the battery. When we installed the HEI module we ran a new wire directly to the fuse box and plugged into the ignition terminal. Also not sure what size the ignition solenoid fuse is supposed to be. I've seen 2 different images of the fuse box. One showed a 10 amp, the other it's a 20 amp.

Amy thoughts?