Alternator
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Freshman User
Joined: Jun 2002
Posts: 28
Likes: 0
From: Mims, Fl.
Alternator
Here we go again. Tried to locate my problem all over the forum
to no avail. What I need is a wiring diagram for my F-100 1978 truck. My alt. lite came on the the other day and it wont go off. Replace the alternator first but that didnt help. The voltage regulator next. That didn't work either. Took the old alternator
back to Autozone, they said it's fine. Put it back on, still no good. Took the new one back to autozone and they said it was bad. Since my old one was good I put it back on... You guessed it, still the lite stays on. Can anyone send me a diagram of the charging circuit with the idiot light PLEASE? If not tell me what to do. All of the connectioms lood like new.
to no avail. What I need is a wiring diagram for my F-100 1978 truck. My alt. lite came on the the other day and it wont go off. Replace the alternator first but that didnt help. The voltage regulator next. That didn't work either. Took the old alternator
back to Autozone, they said it's fine. Put it back on, still no good. Took the new one back to autozone and they said it was bad. Since my old one was good I put it back on... You guessed it, still the lite stays on. Can anyone send me a diagram of the charging circuit with the idiot light PLEASE? If not tell me what to do. All of the connectioms lood like new.
Post Fiend
Joined: Apr 2002
Posts: 7,157
Likes: 1
From: Central Kali
Alternator
A reliable fix is to connect a wire from the run position on the ign switch to the S terminal on the voltage regulator. When the S terminal has +12 on it, the regulator provides voltage to the field terminal of the alternator which then starts putting out 14 volts.
Then install a voltmeter so you will know that your alternator is working. The idiot light setup is just a different way of getting the regulator going.
Handy tip, If you are not charging, check the voltage at the field terminal. If you have approx 12 volts, the alternator is bad. If no voltage, the regulator or it's input to S or I is not there. The I terminal is not used with ammeter equipped trucks.
Then install a voltmeter so you will know that your alternator is working. The idiot light setup is just a different way of getting the regulator going.
Handy tip, If you are not charging, check the voltage at the field terminal. If you have approx 12 volts, the alternator is bad. If no voltage, the regulator or it's input to S or I is not there. The I terminal is not used with ammeter equipped trucks.
Freshman User
Joined: Mar 2003
Posts: 26
Likes: 0
Alternator
Peterson recommends avoiding Duralast products. Go to Auto Zone and buy a Haynes repair manual. The wiring diagrams are in the back. I think the book costs $14.88. Watch out, the diagrams are very complicated to read. Maybe try an aftermarket amp gauge.
