another charging prob
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New User
Joined: Apr 2006
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From: Bozeman, MT
another charging prob
I have a '79 f-150, 351M
99% original including wiring
The problem:
while running at idle the voltmeter reads 12.5
at about 2000 rpm, 12.9
while running at idle with the lights on, 12.2
I have switched or replaced (from working pickup) battery, alternator, voltage regulator, ignition module, coil
and
ran new ground wires from battery to engine, battery to alternator, and battery to voltage regulator and unpluged voltage regulator and ran a wire from 'F' terminal to battery, after all this, nothing changed.
help
99% original including wiring
The problem:
while running at idle the voltmeter reads 12.5
at about 2000 rpm, 12.9
while running at idle with the lights on, 12.2
I have switched or replaced (from working pickup) battery, alternator, voltage regulator, ignition module, coil
and
ran new ground wires from battery to engine, battery to alternator, and battery to voltage regulator and unpluged voltage regulator and ran a wire from 'F' terminal to battery, after all this, nothing changed.
help
Moderator
Joined: Jan 2001
Posts: 56,971
Likes: 2,731
From: Virginia
Take your voltmeter and put the negative probe on the battery -, and put the + probe on the large output lug on the back of the alternator. You should get 12 volts. If you don't there is a fusible link in the output wire of the alternator that has burnt in two. Follow that wire up through the harness and you should run across it.
Moderator
Joined: Jan 2001
Posts: 56,971
Likes: 2,731
From: Virginia
If your truck has a factory ammeter in the dash, then the wiring should look like the diagram below. Turn the key to run, and see if you get 12 volts on the "s" terminal of the regulator. If you have a factory "alt" light in the dash, then I have a different diagram.
Moderator
Joined: Jan 2001
Posts: 56,971
Likes: 2,731
From: Virginia
With the engine running, what voltage do you have on the "F" terminal of the alternator? Be careful and don't get caught up in the belt or fan.
Or, run a wire from the "F" terminal of the alternator, and with the truck running, touch the "F" wire to the battery +. The alternator should go to wide open charge, and the voltage on the battery should jump up.
Or, run a wire from the "F" terminal of the alternator, and with the truck running, touch the "F" wire to the battery +. The alternator should go to wide open charge, and the voltage on the battery should jump up.
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