‘87 V20 Alternator / Battery Wiring - Will not charge!

[FoxCustom]

Originally Posted by Dead Parrot

Another reason for an isolator might be to power something only when the alternator is providing charge. Whatever that blue(gray?) wire is going to across the top of the relay/fuse combo might drain the battery if hooked direct to power.

Chasing mystery circuits installed by a PO can be so much fun!

Also possible the PO was having a stealth leaky circuit and used the isolator to prevent having a dead battery every morning.

WE HAVE SUCCESS!!!! Starting strong and charging great at 13+ volts!!!!

I removed the isolator, repaired a couple frayed (nasty) wires down at the starter, and rerouted all the alt / batt wires to a factory arrangement.

Dead Parrot, I had thought that at first too but that blueish wire was running all the way to the rear bumper area of the truck... I believe the truck was set up as an in bed camper hauler with some fifth wheel duty back in the day.

Relieved to have my truck back in action! Thank you for the clues, guys!