Flummoxed - alternator not charging - JeepForum.com
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post #1 of 3 Old 05-12-2015, 06:59 PM Thread Starter
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1970 CJ5 
Join Date: Aug 2012
Location: Leonardtown
Posts: 6
Flummoxed - alternator not charging

So I decided my Summer project was to clean my engine compartment. Before the weather turned warm my idiot light - amp light on the cluster - came on.

Jeep = 1970 CJ5, 225 v6, all original but the wiring looks to be a replacement from about 20+ years ago. New battery this late Winter.

So I followed the FSM troubleshooting guide pages 195-197 section H. It passed the isolation diode - shorted diode test but failed the open diode test. Couldn't find a replacement anywhere on the net so I replaced the alternator. New alt is a Remy 20170. External voltage regulator.

Installed new alt and fired up the Jeep. Ran great, better that before, but the light remained on. Took her for drive to get the RPM up and yep, the light goes out. Great news...

A week later the light comes on again. So I run the tests again and this time it fails the voltage regulator test. So I buy a replacement.

Installed the new regulator, no joy, and now the tests make no sense.
Engine off - aux voltage is 0, output voltage is 12.4v
Engine on - aux voltage is 2.5-2.6v variable, output is 12.4v

Disconnected the voltage regulator, jumper from aux to field; aux voltage is 12.3v steady, output is 12.4v.

Did a ton of reading on this forum, searching for anything. Checked all the wires for continuity, replaced all the connectors, and removed the starter, cleaned the terminals and installed a new fuse link. Also set up grounds per Jeephammer's guide to ensure the shortest links between battery and alt.

No change! Voltages still the same, but I have to say it starts much faster and runs a bit smoother. Cold start now only takes a quick touch of the starter key.

What am I missing?


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post #2 of 3 Old 05-13-2015, 09:25 AM
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1980 CJ7 
Join Date: Dec 2007
Location: Killeen
Posts: 1,423
A voltmeter. I don't trust idiot lights.
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post #3 of 3 Old 05-13-2015, 02:36 PM Thread Starter
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1970 CJ5 
Join Date: Aug 2012
Location: Leonardtown
Posts: 6
As an update, I jumpered the field to output and with VR disconnected measured the voltage across the battery. Started at 13v and steadily climbed to 15.5v over about a minute. That tells me the alt is ok and my new VR must be bad.

New VR en route...

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alternator , cj5 , not charging

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