1990 pickup won't start. Blown 80 amp fuse
10-04-2017, 10:09 PM
#1
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1990 pickup won't start. Blown 80 amp fuse
I was driving to go pickup a co worker. And just before I got there. All my dash lights when out along with my radio. My gauges went down, but my speedometer kept track of the speed. Only the charge light came on on the dash. My headlights work, tail lights and brake lights don't. Dome light works, also makes a buzzing sound when key is in the ignition. Got to work without turning my truck off (fear of not being able to start it again) turned it off and now not able to start it. Main 80 amp fuse was blown. I had a friend get a new one. Replaced it. And it blew again. I've checked all my ground wires. None (that I know of) are exposed and grounding somewhere else. I have recently done starter and alternator work. Checked all the areas around them. No grounding. Also when I tested the polarity of the battery. It was switched. In the middle of me working on it. The polarity switched back. Then went back to being reversed. Have no idea what has happened. Only truck to get around with right now. Any information would be helpful.
10-05-2017, 09:21 AM
#3
O.P.
How sure are you about your alternator work? New? Rebuilt? Disconnect the "B" wire from the stud terminal of alternator (here) and measure resistance from stud terminal to ground. You should have very high resistance (I don't remember exactly but should be tens of mega-ohms). Low resistance means bad rectifier or short in alternator.
Double check your wires, especially the thick "B" alt-to-batt wire and the thin white "S" wire that goes into the alternator connector. You sure nothing is shorting to the alternator stud terminal? On the first-gen 22R-E (schematic here), "B" or "S" wire shorting to ground will blow 80-Amp fuse and no other fuse. "S" wire, the thin white wire going to the alternator connector is spliced into the "B" wire near the the battery.
Last edited by RAD4Runner; 10-05-2017 at 09:25 AM.
10-05-2017, 11:17 AM
#4
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Undid the stud to my alternator. My charge light went off. Still getting the buzzing with a working dome light. Went and tested the battery and it was fine. (Polarity not switched I guess) going to get a new alternator soon. Looked at all wires none were open and or grounded some other place. Tore open all wire harness. Gotta retape everything back to where it was after I'm finished. Will post when done and fixed. 80 amp fuse didn't blow after I plugged it in and the alternator was taken off though.
10-05-2017, 05:22 PM
#7
Yes... 13V is too low.
To be exact... 13.5 to 15.1V (depending on temperature).
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10-05-2017, 11:58 PM
#8
Something caused that 80 amp fuse to open and it had to be a pretty good draw to do so.
Loose connection any arc marks on the B terminal from being loose ??
Positive cable connection to the starter another likely place
Depending on the quality of the rebuild 13VDC is well within what I have seen as of late
Loose connection any arc marks on the B terminal from being loose ??
Positive cable connection to the starter another likely place
Depending on the quality of the rebuild 13VDC is well within what I have seen as of late
10-07-2017, 11:14 PM
#10
However..
A loose connection may cause overheating of connections but not enough to blow an 80-Amp fuse. I suggest you double-check your wires.
10-08-2017, 01:38 AM
#11
I will call you on that Ray a loose enough connection on one of those cables The B Terminal of the Alternator or the positive battery cable will cause a large enough arc to easily open the 80 amp fuse .
Having repaired it a few times
Then the fact of the studs being pretty much melted off is a good sign.
Although it can be any of a 100 other things as well
Having repaired it a few times
Then the fact of the studs being pretty much melted off is a good sign.
Although it can be any of a 100 other things as well
10-08-2017, 06:34 AM
#12
But the O.P. never mentioned what the stud's condition is like. That's why I always stress, " A problem well-stated is a problem almost solved," AND "A picture paints a thousand words."
