Hey guys, haven't been around here for awhile. I recently have started having electrical troubles with my 88 250 7.3 about 2 years ago I did a 3G alt conversion and have had no issues until now. it all started about 3 months ago. GP controller died. would not cycle gp's it would just flash the WTS light once, replaced the controller, problem solved. drive it for a month or so Batt light comes on, stays on a little while then when off. truck was charging. a few weeks ago. the batt light would come on when I started the truck and stay on until I was half way to work, about 20 min, then go off. did this to and from work for a few days then quit. in the mean while the truck was starting hard, turning over slow. tested batts, test good. alt is charging, cleand batt connections and it fixed it for a few days, then back to normal slow cranking, and the headlights dim a little when I push in the clutch and the engine revs slow when I downshift. fast forward to last light. truck was plugged in yesterday morning, drive to work, no issues. sat 10 hours at work, go to start it, not plugged in, cranked extreamly slow, it was 10 degrees, but started, idled for 10 min, got in it turned the heater motor on hi head lights on, it was 2 am, pulled out on the road all was good, I just shifted into 3rd gear, then everything goes dim, really dim, volt meter pins to discharge, WTS light flickered on and off and then stayed on and the truck died. get it off the road, turn the key off, everything shuts off like it should pop the hood, nothing is clearly shorted, nothing burnt, nothing hot, no smell, nothing out of the ordinary. marker lights were bright, I unhooked the Red wire to the GP's from the controller relay just to be sure, no arc or nothing so it wasn't energized. hit the key, truck fired up and everything was fine. hooked the GP's back up when I got home, sat all night drove it today. Batt light stays on constantly now, alt is charging. output was 14 volts across the pass batt 13 across the drivers. and about 12 amps checked with a clamp on amp meter from the batt lead from the alternator.
any ideas?

 

This will sound repetitive, but check your grounds, all of them. Block to frame, block to cab, all of 'em. With electrical when something weird is going on, every thing's wired correctly and tests out good, it's usually a ground problem.

 

I planned to do it again, but I don't think bad grounds would cause a relay to randomly energise. ill pull it in the shop this weekend and do a little pokeing around