1990 Charging System Problem
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From: MENDON, MI
1990 Charging System Problem
I have A 1990 f-150 5.0L 2x4. Battery is good, alternator good (bench tested twice @ different stores) and still the battery idiot light is on also the amp gauge is reading low output. when testing with the meter it reads battery good but charging system problem. Does anyone have any idea where the problem is? Where would be the best place to start? Thanks in advance.
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From: Minneapolis, MN
1990 Charging System Problem
Are you checking the fusible link by continuity (+12 volts at the main terminal on the alternator) or just visually? Most of the time, the fusible link will burn open inside the insulation with little or no indication externally. Sometimes if you flex or pull on the wire you can feel a weak spot.
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From: MENDON, MI
1990 Charging System Problem
The fuselink tested fine.
I did notice there are several fuselinks around the cylinoid (sp). those also appear (visual) to be alright. Any other ideas? Thanks guys for the help.
I did notice there are several fuselinks around the cylinoid (sp). those also appear (visual) to be alright. Any other ideas? Thanks guys for the help.
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Have you ever replaced the plugs that plug into the alternator? If no, then do it immediately. They get loose over time, the looseness causes resistance and heat. Not uncommon for the Alternator harness to catch fire on this model truck.
If you have a multimeter check the alternator to solenoid harness for resistance. If the alternator is good and the battery is good, then it has to be in the wires.
Good luck
If you have a multimeter check the alternator to solenoid harness for resistance. If the alternator is good and the battery is good, then it has to be in the wires.
Good luck
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From: MENDON, MI
aelliott thanks for the reply. I finally took the truck to a mechanic, $100.00 later it seems the alternator was bad? Funny how his garage is just across the street from Napa where I bought it and also one of the store's that tested it and said it was OK? I did go to the junk yard and picked up another harness ($16.00) when it did'nt fix the problem I had the original one tested (duh) it was fine. Wish I had seen your post sooner, I'm not a mechanic but I could not figure out how there could be a short down stream from the starter relay and have it affect charging and not drain the battery when setting. Oh well live and learn. Again thanks for the reply. Mark
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