How does the 3-pin CD unit fail? What to replace with?

[Sunroof]

I had another humdinger afternoon drive today with plenty of suspense. After a nice 20 mile romp about town with excellent performance, the old girl (1973.5T) decides to poop out at the light at a busy intersection. I started it back up and limped into a mall parking lot. Fuel pump was humming but no noise or vibration from the CD unit. I could not locate any fuse or relay that might protect the CD unit in my manual. Are they circuit protected?

Up shows the tow truck (very cool dolly system by the way) and we get it back home. As soon as I roll the car into the garage (7 mile tow distance and an hour later), she starts back up!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

So the question is can a CD keep kicking on and off before giving up the ghost? Just how do they fail? Could the cooling of the engine help ignite it back up? I need to get some ideas before taking it on the road again. With my luck its probably not even related to the CD unit!!

Thanks

Bob
73.5T

[john walker's workshop]

they can be heat sensitive. send it to loren (lorenfb here) @ systems consulting for new guts. you should keep the original unit, if it's bosch, because everything else is grade B quality or below.

[Sunroof]

John,

First thanks for chiming in. If they are heat sensitive then I certainly cannot afford continuous breakdowns like this as we approach the summer. This is the first time it has happened in a decade, so is it a sign that the CD is on the way out?

I was advised that converting to the MSD ignition with built in rev-limiter (6AL-6425) is the smart and cost effective way to go moving forward. Would you recommend this choice as well?

I was also told to avoid Permatune replacements.

Opinions, please.

Thanks,

Bob

[rpmgroup]

I have used both permatune and bosch boxes that have failed. current permatune box going on 8 years but i alway carry a spare and i would carry one if i was using bosch. i have found bad ground wirirng and wiring to the dist having cause my units to stop working

[Sunroof]

Thanks. You might be right on the wiring as that infamous "green" wire running off the dist is always a topic of debate. That original Cd unit has been sharing that hot engine compartment since it left the factory in 1973 and I know characteristically it will heat up and shut off again. Maybe not tomorrow or in a week but for sure again!

I am torn between these rebuilders and the MSD unit. Looking for a consensus on the issue.........one rebuilder offers a ten year warranty.

Bob