Author Topic: 1980 20r 4x4 Alternator Wiring Madnesssss  (Read 68 times)

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  • Offline Dusty Trails
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1980 20r 4x4 Alternator Wiring Madnesssss
« on: Jul 29, 2020, 06:18:39 PM »
Howdy Guys. So I have a 1980 4x4 pickup and I'm trying to sort out why the alternator is not charging. 12.7 Volts key off, 12.4 volts running. B connection (fat charging wire) on the back of alternator with key off has power to it 12.7 volts. 12.4 while running. So it looks like the connection is clean to the battery. It's a refurbed 55amp Ultima alternator. I've already taken it back to O'reillys and had the alternator tested and it's good. I suspect the culprit is the IC regulator. My big problem is finding out what wires go where. Specifically at the  fat green connector to the regulator I need to know where the green blue and black wires connect to the alternator. I've been using a Haynes manual and I don't trust the diagram. The original plug that went to the back of the alternator was missing and of course it had random wires and connectors on it. When I pulled off the old one I could not see the order that they were in and now here we are. Supposedly a 1980 4x4 had a LEF style alternator and thats what this ultima is. If any of you fine folks have an 80 4x4 sitting around I sure would love a pic or diagram or ANYTHING about this. Thanks! :hammerhead:


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Re: 1980 20r 4x4 Alternator Wiring Madnesssss
« Reply #1 on: Jul 29, 2020, 06:43:25 PM »
L (Lt Blue) wire: From "N" to voltage reg
G (Green) wire: From "F" to voltage reg
B (Black) wire: From "E" to voltage reg
W (White) wire: From "B" post to battery (should be red .85 fusible link on this wire at the battery - it will likely be in plug with a green .5 fusible link)

If you have it right, BEFORE you turn on the ignition:
-The White wire ("B" post) should be hot

When you turn to ACC:
-The charge light should and either the Blue wire ("N" terminal) or the Black wire ("E" terminal) should be hot - not sure which one though

When you turn engine to the ON position:
-The Green wire ("F" terminal) should come hot

Before anything though, I would check to make sure your fusible links aren't fried and that your charge light relay works - you truck will not charge without either of these.
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