[ProStreet67]

Sounds like Hank has the right plan of attack. Its def power related as Hank said since you loose all power and or crazy things start going on prior to the total outtage. Either a loose connection or a fusable link somewhere. As Hank said you will need a meter. A test light will only show power is present, not how much.

I would suggest starting the car and manually follow all the positive cables from the battery and shake/move them while the car is running. I would bet you will find the culprit in short order, if not do the same while taking readings with the volt meter.

I have also had the wiring inside a jacket break from being bent and or vibrated and over time enough strands broke to cause an issue. Also check the terminals on the battery cables, they sometimes can be bad too. Electrical gremlins are fun.... NOT !

My son had something similar issue on his GMC truck and the positive cable was close to and at times laid on the header tube as the cable was not secured, it would ground out and not let him start the truck or provide power to the vehicle. Eventually the fusable link blew. It should have much earlier on but it didnt......