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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 Topic: alt light glows when running
    Posted: May/16/2018 at 7:20am
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomslik Quote  Post ReplyReply Direct Link To This Post Posted: May/16/2018 at 5:47am
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...

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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 9:45pm
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.

Bruce Clarkson
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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 8:14pm
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 6768rogues Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2018 at 6:48pm
Dealers used to take out the bulb and paint it black, then put it back in. No more glow.
Content intended for mature audiences. If you experience nausea or diarrhea, stop reading and seek medical attention.

Located usually near Rochester, NY and sometimes central FL.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomslik Quote  Post ReplyReply Direct Link To This Post Posted: May/13/2018 at 7:12am
Build, you MAY have solved my problem, I replaced the bulbs with p194's when I had the dash out


off we go to the parts store!

i'll let ya know if and how it works

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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/12/2018 at 11:14pm
I found another post I made - a sticky, that outlines the testing, etc. for all this - o
According to AMC, replace the original equipment #158 bulb with their service replacement, bulb number 1445.
But their kit also included a different socket as the bulbs were different. So AMC said if all else is well, maybe they should have used a different bulb.

I also outlined the test procedure and items to check (among other things to check) in this post - 
http://theamcforum.com/FORUM/alternator-charging-system-tests-for-amc-vehicles_topic74295_post807525.html#807525

The kicker is this - in 71 and later cars AMC was using Motorola alternators with the SAME diode configuration as GM - meaning that even with a GM alternator the light could glow if the cause was not the diode trio, or as Motorola called it, the field diode. It was actually wired much like the GM of the same era. GM, Ford and Chrysler were nearly TEN years behind AMC on charging systems (thank Motorola and AMC's foresight for that)
I used to stock a half dozen of those for GM alternators............ why? Because the alt light glowed!
In fact one of the most commonly replaced parts in GM alternators was that diode array - the 10si's used to go through a lot of parts. 

By the way - I don't know what the "reman" alternators use but it's possible they use really cheap electronics (diodes, etc.) and even a reman may be outside of the .6v spec mentioned. I use NOS original AMC and Motrola parts as far as field diodes. (until I run out, that is) and I test each unit not only for output, but for voltage drop and more across diodes, isolation diodes, field diodes (diode trio) and such. My test setup I made also includes a BULB just like AMC used (in fact it's from an AMC instrument cluster) and wired just like as in the car. This way I can check not only for proper output, but silly little things like "does the light glow?"


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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/12/2018 at 9:26pm
Originally posted by 71 Javelin AMX O.O. 71 Javelin AMX O.O. wrote:

I'm still trying to get an answer on why my dash lights go dim when I have the car in drive at a stop light, idling. The alt gage swings to the minus side of the gage, but when I put it in nutrual the gage goes to the middle and the dash lights come back.  Stock restoration on a 1971 Javelin AMX 401 auto borg warner M12
Steve

Different topic - please start a different thread on this if you haven't already.

And yes, I already mentioned the service bulletin - TB11 7100 series  April 19, 1971

Volt meter on a low range (so it can read fractions of a volt)
Start engine, ALL accessories and lights OFF
Connect + lead of volt meter to output of alternator
Connect - lead of volt meter to the aux or reg terminal of the alternator (where the orange wire is connected)
Read the volt meter - if it reads over .6 volts, you have a problem field diode (diode trio)
If it reads LESS THAN .6 volts, the alternator is NOT the problem - your WIRING or dash bulb is.
When I say wiring, believe it or not, the IGNITION switch could be the problem, fuse panel issue, printed circuit, wrong bulb, main harness connector, connection at the starter relay (battery side) main harness firewall connector, etc.
The problem is everyone blames the alternator automatically when on a 40 year old car you have over a DOZEN possible causes - and it's usually honestly connection type issues, or the ign switch and so on. And what happens is that IN THE PROCESS of replacing the alternator and regulator, they unwittingly fix the REAL problem, such as a connection, but don't know it so they say it was the alternator or regulator.

I can't re-find the other TSB that tells about the different bulb-  I've misplaced it - bummer.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote george w Quote  Post ReplyReply Direct Link To This Post Posted: May/12/2018 at 9:06pm
Idle speed could be too low or too much current draw.
Any aftermarket items like special lights, stereo amps, etc ?
Do you have A/C and is in in use when this happens ? High blower speed also has high current draw. Battery should be in tip top shape and ALL connections: battery cables, starter relay, starter, alternator wiring connections, engine block to cross member jumper should all be checked, cleaned with a wire brush and tight. Battery disconnected of course when cleaning.
Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 71 Javelin AMX O.O. Quote  Post ReplyReply Direct Link To This Post Posted: May/12/2018 at 8:40pm
I'm still trying to get an answer on why my dash lights go dim when I have the car in drive at a stop light, idling. The alt gage swings to the minus side of the gage, but when I put it in nutrual the gage goes to the middle and the dash lights come back.  Stock restoration on a 1971 Javelin AMX 401 auto borg warner M12
Steve
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