My 3400 swapped 86 2m4 has developed an electrical issue that has stranded my daughter three times over the past few months. My daughter is getting reluctant to drive it and I fear that if I don't figure out what's wrong, my wife is going to make me to sell it.

Here's what is happening- I have a volt gauge installed which normally reads 12.5 v with the engine off and between 13.5 and 14 v when running- so I know the alternator is wired correctly. But on three occasions so far, after starting the car to head home from work, the gauge read only 11 or 12v and she said it slowly dropped as she drove home. Each time this happened was at night so she had the headlights on. Once the volts dropped below 10, the car died- lights, radio, everything. No clicks when turning the key to start, etc. Nothing, just dead. However, after the 1/2 hour or so tow ride home, the car started right up, volt gauge showed 13.5-14 and everything appeared normal.

The latest incident was last night and by some mercy of the car gods, the tow truck driver just happened to be right behind her so he saw what happened- he said he could see the tail lights flickering then go out, so that suggests it's a fundamental power issue. The battery, the alternator, the starter and all of the wiring between those components were brand new when the 3400 swap was installed about 6 months ago and after each episode, I checked, cleaned and re-tightened all of the connections. I'm confident this isn't just a bad connection. Something is obviously getting hot with the extra current draw of the headlights- could the fusible links that run from the 2 post junction block forward to the rest of the car be slowly failing so that as they heat up, they cut off all current from the positive side of the battery?

HII would be checking all your body and engine grounds. also double check battery cables. Not llikely Belt slipping but check. seems like alternator is loosing connectivity and so dosen't have power to excite it to charge.

ALSO, I would test/measure the battery...

A fully charged battery must read 12.5 volts or better.
A 'weak' battery can 'look like' it is okay but will not power the car too long when under a load.
If the battery won't hold 12.5V - replace it

With a known good battery, measure the voltage at the battery as the car is running and the headlights are ON.
Use a voltmeter to measure the battery at idle AND 3k RPM
As you know; a good generator/alternator will put out 13.5 volts to 14.5 volts

BTW: Fusible links are like a fuse; when they blow, it is "light out" until they're replaced....

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles