1985 F150

Asked by Nov 19, 2019 at 01:24 PM about the 1985 Ford F-150

Question type: Maintenance & Repair

Checked all wiring, fuse links etc and all was well.
Has new alternator and battery but wouldn't
charge. Traced it to a bad voltage regulator and
replaced with new. It charges just fine but after the
new regulator was installed the engine runs rough,
misses and wont accelerate ?
I unhook the regulator and it runs just fine ???

There has been no wiring hacks from the previous
owner related to the entire alternator/charging
system (i just bought the truck) but this is baffling
me.

3 Answers

154,355

ok so you replaced the alternator with a new one correct ? if so did the new alternator have a integral regulator in it ? did the old one have this. if it didn't you may have gotten the wrong alternator. Also try adding a thick wire like 00 wire from the motor to the body.

Same alternator (3 wire system) and the regulator was screwed to the fender just under the starter solenoid, its all original. There is isnt a ground lug for the alternator but i tried grounding it anyway. It made no difference. When the bad voltage regulator was in it ran fine but didn't charge. New voltage regulator (exactly like the one that i took out) and it charges but the engine just doesn't run right. Again, when i unhook it it runs and drive fine, of course until the battery runs down. When initially diagnosing i did the regulator bypass to make sure the alternator was charging the battery, and it was. I did notice that when i jumped the regulator that it suddenly didnt run right but when i pulled the jumper off it ran fine again, like with the bad regulator on. Wasnt sure what to make of that at the time but the regulator was obviously bad.

Oh, I went ahead and removed the alternator just to be triple sure of everything. Couldn't see the back all that well because it mounted in an obscure place. Anyway all wiring was fine and on the proper poles and I did see a lug actually marked GRD so i ran a large wire from that to the frame (same spot as the battery and block ground. It made no difference as far as running. You hit the gas and it misses, sputters, etc. its very rough and I get a little backfire/popping from the exhaust. It acts like misfire, like crossed plug wires sound when you hit the gas.

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