Hello Everyone, I have a '89 Bronco II 4x4, 2.9L. It has an electrical problem that I need help with. When the engine is cold, the dash panel voltage indicator stays "centerline" like is should. When the vehicle warms up after 5 min. or a short drive, it shows negative, almost to the "10 volt white line". I tried to take a trip from Jacksonville FL to Savanah GA (175 miles), but barely made it 100 miles before the battery died, quite suddenly. I made it back to Jacksonville, 20-30 miles at a time with a vehicle following me for jumpstarts and charges. I recently replaced the alternator, battery, starter relay, and negative battery cable. I had the alternater and battery tested after the system failure, both were functioning properly, except the battery wasn't getting the full charge from the alternator. The mechanic suggested wiring problems. It still has the steady voltage drain after warmup. I've pulled all non-esential fuses from under the dash and hood, problem still exist. I have a wiring diagram and I'm going to start chasing wires in the charging system. Any suggestions or comments would be greatly appreciated.

 

ther should be a screw on the back of the alt that is marked F. if you ground that screw the alternator will be "full fielded", in otherwords it will put out max amperage. I would start by doing that and see if it will charge. If that does work, then check the LG/R wire, it should be 12 volts with the engine running. If it is not, put 12 volts there through a test light (hook one end of test light to B+ and touch the lg/r wire with the other) and see if it starts to charge.

 

Problem Fixed! I did an undervoltage test as per the Haynes Manual, and it indicated a faulty intragal regulator. Replaced alternator - problem solved. Thanks for the help and advice.

 

Glad to hear you found the problem.