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Alt light is on/ ignition off |
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jav70
AMC Nut Joined: Apr/20/2008 Location: New Jersey Status: Offline Points: 257 |
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Posted: Sep/10/2014 at 4:31pm |
Help..Just had my alternator rebuilt. When the ignition is in the off position the alt light is on. Turn it to on, and the light goes out. It is also out when the car is running. Voltage regulator?
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AMC1970 javelin,1968 AMX 343, 1968 AMX 390
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purple72Gremlin
AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16591 |
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Think its the diodes in the alternator.
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amcglass
AMC Addicted Joined: Dec/11/2011 Location: NW Ohio Status: Offline Points: 2588 |
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Diodes I would think is a good place to start
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Javmanpres
BBG Mark Donohue 401 74 Jav/AMX 71 Matador 2dr sedan delivery wagon 1902 Rambler Runabout 70 T/A Javelin |
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rocklandrambler
AMC Addicted Joined: Feb/09/2013 Location: Nanuet, NY Status: Offline Points: 3953 |
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Just take it back to whoever rebuilt it and tell them the problem.
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Past AMC's
1974 Hornet X (new) 1975 Gremlin X (new) 1964 Classic 660 Cross Country 1965 American 440-H |
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FuzzFace2
AMC Addicted Joined: Jul/05/2007 Location: Angier, N.C. Status: Offline Points: 10343 |
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I would also think the same as the others and to take it back but I would re-check to make sure you have the wiring right.
Dave ---- |
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TSM = Technical Service Manual
75 Gremlin X v8 for sale 70 Javelin 360/auto drag car 70 Javelin 360/T5 Street car |
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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Which alternator - 35 or 55 amp?
The 35 amp has a single isolation diode, the 55 amp a dual diode array. The 35's single diode is more simple in its mounting. The 55 is shifted to 180 degrees from the brushes and spans the negative diode mounting studs for its own mounting. If they messed up the insulators there it would likely burn out the internal diodes as it would short the output of the alternator. But in that case it would not charge. The orange wire that comes from the dash ALT light connects to the positive diode array inside. The diodes normally block flow from the ignition switch through the light and to ground. With the switch off there's no power to the light so even a bad diode would simply ground the outside of the bulb, not power it. There would have to be power to the bulb somehow to have an internal diode cause this on 1970 and prior years. HOWEVER, the isolation diode could do this - it's the only thing between that orange wire from the bulb and battery power. If the isolation diode was "bad" in a shorted way, then battery voltage via the output terminal could get to the orange wire, to the bulb where it would ground through one of the other items that's sharing the connection with the bulb at the ignition switch. To test for that possibility, disconnect the battery wire from the alternator and see if the light goes out. If so then the isolation diode is shorted and not isolating. The bulb needs 2 things to light - power on one side, ground on the other. IF the key is off, there's no power on the key side. However, there MAY be ground on the key side through other bulbs or devices that share the spot on the ignition switch where that bulb normally gets power from. OK, assuming that with the key off the inside can't power it, but the inside may ground it, that means there's power getting to it from the outside - the engine bay area. And the most likely spot for that is the isolation diode. To test - car not running, key off, bulb lit, disconnect the voltage regulator connector at the regulator. Is the bulb still on? IF so, then it's not regulator. If not, then it's regulator. Reconnect regulator, car not running, key off, CAREFULLY disconnect the battery wire from the alternator output stud. Did the light go out? If so, it's a bad isolation diode. If not, then look for a mouse with insulation hanging out of its mouth.............. (Or compare your wiring to some of the pictures posted recently in this area.) |
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jav70
AMC Nut Joined: Apr/20/2008 Location: New Jersey Status: Offline Points: 257 |
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I decided to use it as a core and bought a reman at NAPA. The place that rebuilt it was close to where I work, which is an hour from home, and sort of out of the way. Installed the NAPA unit and everything is good! Thanks for the replies.
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AMC1970 javelin,1968 AMX 343, 1968 AMX 390
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jav70
AMC Nut Joined: Apr/20/2008 Location: New Jersey Status: Offline Points: 257 |
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To Bill D...Excellent reply. I will print that out and keep it in my Service Manual for the future. Thanks!
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AMC1970 javelin,1968 AMX 343, 1968 AMX 390
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davester304
AMC Addicted Joined: Apr/05/2011 Location: Victoria BC Status: Offline Points: 621 |
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Just jumping in on this thread - sort of have the opposite. Got the Alternator checked - all good including the diode(s) - all worked fine for a few days, now, no Alt light with key turned on (not to start position) -until then the light came on and then started fine. Still started but now looks like no juice going back into the battery from the Alt - I am thinking it is the Voltage Regulator no longer doing its job? Got stranded at the gas station on my way to a show on the weekend too! Jumped it and got home no problem. I have been having issues lately - that seemed to be solved for a few days - if you have read my other postings in this category.
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1970 Javelin SST
If you don't look back at it when you park it, you bought the wrong car |
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carnuck
AMC Addicted Joined: Mar/31/2010 Location: Seattle Status: Offline Points: 3942 |
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Could be the sensor wire at the connector broke.
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