GEN light stays on dim
#1
Le Mans Master
Thread Starter
GEN light stays on dim
It lights full power when first started like it's supposed to, then stays on about 1/2 lit. This just started this morning. The dash volt meter is reading right at 13 volts, or slightly below, and was verified correct by my multimeter. I had the battery checked at Advance auto today, they said it bad, and fortunately got a free repolacement. That didn't fix it, so I carried the alternator there, and it worked perfect on the bench tester. Then took the car up there, and the system wasn't putting out enough volts. So far I've cleaned and reinstalled the battery main ground to the frame, and will go after the other main grounds tomorrow. Also the tach will bury to the right when I turn the car off, it didn't do that before. When you first start driving it will stay buried, but after a very short while it will free itself and work normally. Any other things I should be checking, or any other ideas?
#3
Le Mans Master
Thread Starter
But this is the same alternator that's been on the car for years and has never been a problem. I've not added anything to create more electical draw.
#5
Racer
Member Since: May 2007
Location: Cherry Hill N.J.
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GEN light
Check the plugs and wires connected to the alternator..
The wires breakdown at the plugs due to the vibration of the alternator.
The plugs corrode from heat and moisture......
Both are simple fixes...
Hope this helps............Good Luck
The wires breakdown at the plugs due to the vibration of the alternator.
The plugs corrode from heat and moisture......
Both are simple fixes...
Hope this helps............Good Luck
#6
Melting Slicks
That would be my guess. I had the exact problem with my 7 year old alternator. Had it rebuilt and havent had any problems.
If you do a search you will find others who had the same problem. Unfortunately they dont repost to say how it was cured.
#8
Race Director
#9
Le Mans Master
Thread Starter
Ok, the battery shows .4 volts with the cables hooked up and the car not running. If I unhook the cables it shows 12.4 volts, again with the car not running. Also, my multimeter shows .4 volts across the battery cables as the car is running, but the dash voltmeter shows about 13 volts. They both read the same yesterday. Also if I test from the red wire on the back of the alternator, I get 14.66 volts constant with the car running, but it jumps all over the place with the car off, from .4 up to 6 volts. How do you test for a bad diode?
Last edited by C3 4ME; 06-14-2009 at 11:16 AM.
#11
Le Mans Master
Thread Starter
Just got back from carrying the alt. to Auto Zone. Their test said Lamp/Diode trio:Passed, Regulator Test: Passed, Rectifier Test: Passed. Looks like I'm going to be chasing something in the wiring of the car itself.
#13
Le Mans Master
Thread Starter
At the bat + terminal on the alternator, it's 14.66 volts constant with the car running, it jumps all over the place with the car off from .4 to 6 volts.
#14
Race Director
Try this .... remove the 2 wire plug from the alternator and turn the key to ON and watch the gen light. If its half glowing then you have a wiring issue. If the light is not on... then ground the brown wire in the 2 wire plug and see if the light comes on bright.
#15
Le Mans Master
Thread Starter
Ok, with the 2 wire plug disconnected, when I turn the key on, no light at all. When the brown wire is grounded, the light is on full bright. I ran the car again after reinstalling the alternator, and now I think I might be chasing a problem with the light only. I'm now reading 12.4 volts across the battery terminals with the cables hooked up, and 14.5 with the car running, and basically the same numbers when the same test is done from the red wire going to the back of the alternator. I did have the center cluster out over the winter to fix the clock, so maybe there's a problem there. Where is the ground for the center cluster? BTW, I've not had any problem with the car starting, or noticed anything different about how the car is actually running from an electrical standpoint (or any other standpoint for that matter).
Last edited by C3 4ME; 06-14-2009 at 05:38 PM.
#16
Le Mans Master
The alternator light does not need a ground behind the dash.(this is simplified) It has a positive supplied with the key on, the otherside of the bulb goes to the brown wire at the alternator. When the engine is off, the bulb sees enough resistance through the alternator to "ground it" sort of. But when the engine is running and the alternator is charging there is voltage at the terminal for the brown wire, so, the bulb will go off.
#17
Race Director
Ok, with the 2 wire plug disconnected, when I turn the key on, no light at all. When the brown wire is grounded, the light is on full bright. I ran the car again after reinstalling the alternator, and now I think I might be chasing a problem with the light only. I'm now reading 12.4 volts across the battery terminals with the cables hooked up, and 14.5 with the car running, and basically the same numbers when the same test is done from the red wire going to the back of the alternator. I did have the center cluster out over the winter to fix the clock, so maybe there's a problem there. Where is the ground for the center cluster? BTW, I've not had any problem with the car starting, or noticed anything different about how the car is actually running from an electrical standpoint (or any other standpoint for that matter).
#19
Race Director
Here is another little homemade setup that will rule out the dash circuit so you won't have to go digging in there unnecessarily. Both setups will have the light on when the car is not running but once the engine is running both will act just like the dash circuit. If you hook this up and start the engine and the light is on or glows dim you have a problem in the alternator not the dash light circuit.