alt light glows when running
Printed From: TheAMCForum.com
Category: The Garage
Forum Name: Electrical - non engine
Forum Description: Charging systems, lights, non-ignition system, it goes here.
URL: https://theamcforum.com/forum/forum_posts.asp?TID=94121
Printed Date: Apr/19/2024 at 5:52pm
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Topic: alt light glows when running
Posted By: tomslik
Subject: alt light glows when running
Date Posted: May/12/2018 at 12:27pm
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before I switch to a GM alternator as i'm about tired of dealing with a Motorola (US version of lucas;) ), any idea WHY my alt light glows (not full strength) when running? 73 hornet, fwiw... I've changed alternators 3 times, various regulators. has a new BW on there at the moment. charges fine, just can't get the light to go off... ------------- 67 american 290/4speed |
Replies:
Posted By: billd
Date Posted: May/12/2018 at 12:53pm
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HAHAHA - hardly a Lucas. The Motorola are pretty reliable. Back when these were newer, fewer of them gave trouble than the GM of the same time periods. They charge better at idle than similar alternators of their day. The problem is that people ASSUME they are so much different from the others when in fact the circuitry and operations are the same as with ALL B-circuit systems. Operationally there is NO DIFFERENCE AT ALL as far as how they operate, etc. You MUST have a good solid ground wire that runs from the regulator to the alternator. That's the black lead from the regulator. That must be CLEAN and connect solidly. The green wire is the field - it won't cause a light glow or that sort of thing like the black could if not clean and tight. It's likely you have a WIRING issue. That's the most common cause. The issue could be the black from regulator to alternator, or at the fuse panel, or the CLUSTER. If there is a bad connection at the fuse panel of where things connect at the cluster, including the traces that go to the light in the cluster. If your car is a 73 then you have an alternator with NO isolation diode, and with a field diode or "diode trio". The regulator must be matched to the 71 and later Motorola. AMC had some troubles and literally had a service bulletin that gave the methods for testing and if all checked out ok, then there was a LIGHT KIT that contained a different lamp and holder/socket for the cluster to hold the different light. I'll try to scan and post a copy of it later - it's a perfect fit for what you are seeing. Changing alternators - NEW, "reman" (YUK) or used? Correct for 73? The regulator correct for the car? -------------  http://theamcpages.com" rel="nofollow - http://theamcpages.com http://antique-engines.com" rel="nofollow - http://antique-engines.com |
Posted By: tomslik
Date Posted: May/12/2018 at 2:48pm
regulator was looked up for a 73, I can get ya a borg/warner number if you'd like.... 2 used and 2 rebuilt alternators, doubt I could find a new one anyway (this isn't a show car so being 100% resto doesn't matter to me) i'd love to see the tsb's i'd appreciate it! ------------- 67 american 290/4speed |
billd wrote:Posted By: Rebel Machine
Date Posted: May/12/2018 at 4:18pm
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If I recall AMC sent a tech bulletin about the glowing ALT lamp. They said to use a different lamp which had a thicker element so it wouldn't light with a small amount of current running through it. -Steve- |
Posted By: 71 Javelin AMX O.O.
Date Posted: May/12/2018 at 8:40pm
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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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Posted By: george w
Date Posted: May/12/2018 at 9:06pm
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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. |
Posted By: billd
Date Posted: May/12/2018 at 9:26pm
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. ------------- http://theamcpages.com" rel="nofollow - http://theamcpages.com http://antique-engines.com" rel="nofollow - http://antique-engines.com |
Posted By: billd
Date Posted: May/12/2018 at 11:14pm
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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" rel="nofollow - 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?" ------------- http://theamcpages.com" rel="nofollow - http://theamcpages.com http://antique-engines.com" rel="nofollow - http://antique-engines.com |
Posted By: tomslik
Date Posted: May/13/2018 at 7:12am
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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 ------------- 67 american 290/4speed |
Posted By: 6768rogues
Date Posted: May/15/2018 at 6:48pm
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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. |
Posted By: billd
Date Posted: May/15/2018 at 8:14pm
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. ------------- http://theamcpages.com" rel="nofollow - http://theamcpages.com http://antique-engines.com" rel="nofollow - http://antique-engines.com |
Posted By: Bruce Clarkson
Date Posted: May/15/2018 at 9:45pm
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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 ------------- Bruce Clarkson |
Posted By: tomslik
Date Posted: May/16/2018 at 5:47am
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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 |
Posted By: billd
Date Posted: May/16/2018 at 7:20am
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. ------------- http://theamcpages.com" rel="nofollow - http://theamcpages.com http://antique-engines.com" rel="nofollow - http://antique-engines.com |