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ALT light on

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billd View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jun/06/2018 at 3:10pm
Honestly? Motorola are not any more finicky or complex to work on that GM or MOPAR, or Ford, which I find among the most troublesome repairing.

What's happening, if my guess is correct, is that the isolation diode has failed or is failing - and instead of dropping the output by about a volt and preventing power from going back through the system, it's allowing it all with no drop, and likely both directions. 
It may overcharge the battery, depending on the battery you have. Some can handle that, some batteries will not handle it well, depending on battery technology and make-up inside.
After a drive see if the battery feels hot, more than typical or usual, and see if you can tell if it's "boiling" - if there's sort of dampness on the top or signs it's misting out the vents. If it's not how and is staying dry, that's not a conclusive check, but says you aren't fast-cooking it alive.
The 35 should keep up unless you have something like electric fans or extra lighting, that sort of thing. 
The firsrt AMCs with AC and alternators - guess what they ran...... 40 (FORTY) amp. Yup, that was the heavy-duty alternator for AC through about 1967 - it was listed for fleet sales/AC until the 55 amp in 1968.
Are you going to Auburn for AMO?

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White70JavelinSST View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote White70JavelinSST Quote  Post ReplyReply Direct Link To This Post Posted: Jun/18/2018 at 9:38am
What I should have stated and meant when I said finicky was more about the rebuilder guy working on a Motorola.

I've read about rebuilders not getting the diodes replaced and people having the same issues with a rebuilt Motorola ALT as the one they gave back as a core.

Well curiously enough, the fuel gauge started reading empty soon after the ALT light coming on, so I crawled underneath and rotated the connector against the pin on the sending unit. Viola ! the gauge came back to life and reads OK now.

Along with that,  I've now driven the car twice for anywhere from 20 minutes to 30 minutes each time, in town, and the ALT light stays off.

Can a diode function intermittently?

I have a later version 55 AMP Motorola with the red heat sink Diode trio, it needs a cleanup rebuild, will this work with the 70 voltage regulator?


Edited by White70JavelinSST - Jun/18/2018 at 9:56am
70 Javelin SST, second owner, purchased 1972
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