I am re-posting part of earlier post under "Another Mystery Wire".

I thought these two might be related, but now think this latest issue is just another symptom of my bigger, yet unidentified problem.

The mystery wire that other forum members helped me identify was this emission control switch used to activate vacuum advance in 3rd or 4th gear. Originally connected at the other end the intake and distributor...

Here is the rest of the post...

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 continuing 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. We went through a thorough diagnostic, checked all the grounds, cleaned and/or re-wired them. But after trying several times to nail down the issue (and going through a couple more MSD boxes) we eventually replaced the MSD with an HEI ignition control module and installed a new coil. Still had issues blowing HEI modules, so I've also replaced the coil and alternator. That seemed to do it and at this point I was thinking that the problem was a bad voltage regulator. The system 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.... Until...

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. Maybe the the transmission vacuum advance wire had nothing to do with the car dying again, but...

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. It seems like this fuse was connected to the solenoid for the transmission vacuum advance...



Fortunately, I had several spares, but when I the new one made contact, the car jumped like the starter kicked in for a moment, and the new fuse was blown right away. Stupid me I didn't disconnect the battery. So I hit the kill switch and replaced the fuse again. This time when I turned the kill switch back on, the car jumped again, but this time did not blow the fuse. It started right up. I let it idle for a while then turned it around and pulled it into the garage. And now I'm really confused. 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 the RADIO TSC SOL fuse?

.I'm not sure how these cars we're wired from the factory. That is, if the IGN terminal was used for the factory ignition system. 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?
Last edited by DHer67; Yesterday at 11:08 PM.
DHer67 is offline Report Post

 

This is 72 it says 10 amp.
How does car jump if automatic in park or manual in neutral?
Factory did not have anything connected to IGN .
From what I have read the switch on the transmission is a ground so what happened to the other end, is there a bare wire in your engine compartment?
The original system used a temperature sensor and possibly two relays mounted on the firewall.
Really unclear what distributor you are running, HEI with built in coil?
http://repairs.willcoxcorvette.com/w...se-panel-b.jpg

 

"The fuse says 32 v on it. I think its a 20 amp."

32 v is the voltage rating class of the fuse which is typical for 12 volt systems. This is independent of the current rating. Look closely on the metal barrels as there should have been a current rating somewhere....like "20A".

 

Thanks for the replies. I'm still using the MSD Billet distributor. We wired that HEI module to that and have it mounted on the distributor cover.

I tried to find some kind of amperage rating on the fuse, I couldn't make anything out. Or didn't see any other markings

 

I'd be less worried about the correct fuse size than finding your dead short. as other have said its 20A.

The radio fuse is hot during ignition and acc -but not in start- you should not be blowing that fuse.

The ignition terminal - is hot during ignition and start - but not acc.

To me- it sounds like to have the MSD- wired incorrectly to the starter-see pics. Blowing the MSD boxes -more than one means something is wrong...

 

MSD wiring question. With all the shuffling around trying to get the ignition system to work, we cut the small red on the MSD harness to power an HEI module instead. Then one of the mechanics I had working on the car ran a new wire to the IGN terminal on the fuse box. Now I want to replace the MSD box. I can find all of the other wires, but cant seem to find where the other end of the small red wire is. It is cut a ways out from the large connector that goes into the MSD box. You can see it at the bottom of the photo with the end wrapped in electrical tape, next to the two white wires. Where does the other end go? The diagram shows it splitting and connecting to the ignition and the distributor. Not sure where that is.