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alt light glows when running

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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: May/15/2018 at 9:14pm
Originally posted by 6768rogues 6768rogues wrote:

Dealers used to take out the bulb and paint it black, then put it back in. No more glow.

Only those who didn't know what they were doing or didn't want to spend the time to find the REAL cause. Yeah a lot of dealerships hire dopes who once swapped and engine so suddenly were "mechanics". If the alternator itself tests out as in the BOOKS it's almost always a wiring issue (or as according to the TSB, a bulb swap is needed)

We never did that sort of BS - we fixed 'em. If they worked properly when new then there's zero reason they can't be made to work again. the idea is to find "what changed" and with a 40+ year old car it means TIME spent and real troubleshooting.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce Clarkson Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2018 at 10:45pm
On my 67 there is, by design, a small current through the alt lamp. At night with lights low, I can see the lamp faintly glow.

I don't have access to my schematics right new but was there a resistor in parallel with the lamp? dunno. If so if it failed the current through the lamp would be more but the alternator would still work. Can't quite recall and my wiring diagram is in storage.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomslik Quote  Post ReplyReply Direct Link To This Post Posted: May/16/2018 at 6:47am
well guys, as of now, the light is off. replaced the rock auto alt with a different used one (off a 73 ambo) and it's off, the bulb trick didn't work(unfortunately)so I threw this one on so I could send the RA one back for a refund as they had no more of them. good thing they're easy to change;)
I want to drive it some more before I give it the final ok, weather hasn't been too good around here...
67 american 290/4speed
73 hornet X 360/auto
72 hornet wagon 304/auto


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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/16/2018 at 8:20am
Originally posted by Bruce Clarkson Bruce Clarkson wrote:

On my 67 there is, by design, a small current through the alt lamp. At night with lights low, I can see the lamp faintly glow.

I don't have access to my schematics right new but was there a resistor in parallel with the lamp? dunno. If so if it failed the current through the lamp would be more but the alternator would still work. Can't quite recall and my wiring diagram is in storage.

Bruce Clarkson


Nope. that's been "guessed at" or speculated more than once, and I've covered it with schematics, diagrams, etc.
NO resistor.

Also - the glow is NOT NORMAL. Period.
When I test the alternators _I_ restore and rebuild, I use a test setup I made that has a DASH LIGHT bulb and socket included in the circuit. I have a switch to emulate the ignition switch, a bulb wired in just like an AMC would have, and it's wired much like an AMC car.
When I test I cup my hand over the bulb to ensure I don't see even a hint of orange or glow. If I see anything, I test the components again........... and replace as necessary.
The problem - and I mean PROBLEM - with Rockauto and other reman alternators is that they use CHEAP replacement parts often NOT IN SPEC. I don't give a #$$%& what they say about tested output and so on - it's CHEAP STUFF, period.
I have myself found replacement parts I've had to trash (because my sources for some stuff is drying up).
I have a bunch of post-1970 diode trios (field diodes) but isolation diodes are near impossible to get now for a reasonable price. I went through THREE isolation diodes before I found one IN spec - and threw away brand new replacement parts. Do you think they would do that? I threw away 30 bucks of new parts because they were far enough out of spec there was the faintest hint of a glow in the light o my test setup.
I may not be as "cheap" as your fifty buck cheap-@## reman but I can say I test for the operation of the light, not just output. 



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