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alt light glows when running |
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tomslik
AMC Addicted Joined: Mar/07/2008 Location: Colorado Status: Offline Points: 680 |
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Posted: May/12/2018 at 12:27pm |
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... |
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67 american 290/4speed |
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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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? |
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tomslik
AMC Addicted Joined: Mar/07/2008 Location: Colorado Status: Offline Points: 680 |
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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! Edited by tomslik - May/12/2018 at 2:54pm |
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67 american 290/4speed |
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Rebel Machine
AMC Addicted Joined: Jul/03/2007 Location: Western Il Status: Offline Points: 5121 |
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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- |
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71 Javelin AMX O.O.
AMC Addicted Joined: Aug/29/2008 Location: Minnesota Status: Offline Points: 655 |
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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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george w
Supporter of TheAMCForum Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899 |
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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. |
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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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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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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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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 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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tomslik
AMC Addicted Joined: Mar/07/2008 Location: Colorado Status: Offline Points: 680 |
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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 |
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67 american 290/4speed |
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6768rogues
AMC Addicted Joined: Jul/03/2007 Location: United States Status: Offline Points: 6241 |
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Dealers used to take out the bulb and paint it black, then put it back in. No more glow.
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