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Re: Alternator Light Posted by Saana88 [Email] ![]() ![]() ![]() In Reply to: Alternator Light, Jason Carpenter, Wed, 23 Nov 2005 01:34:19 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The alternator light should light up when the key is switched on but the engine is not running.
The alternator light should not light up with the engine running. If it does, your alternator is not working properly, hence the warning light.
If the light turns on when the car is running, your alternator brushes are probably worn down too far. That way they're not able to make contact and your alternator can no longer charge the battery and it eventually dies.
If the light glows dimly when the key is on and the engine is not running, one or more of the diodes internal to the alternator have failed. Even though the brushes may still be good, the alternator can no longer charge the battery and it dies.
If the light does not light up when the key is on and the engine is not running, check the single wire (I think it's green) going to the back of the alternator and be sure it wasn't accidentally knocked off during an oil change. Be sure it is making good contact.
If the light does not light up when the key is on and the engine is not running and you've checked the connector at the alternator, either your bulb on the dash is blown or your battery is very weak.
The alternator warning light bulb has a different resistance value than the other warning and instrument bulbs. I learned this the hard way. When my voltage regulator brushes wore down, the light came on, and I drove the car a few times. (I have an unusually overrated battery.) After a while the light went out, and I figured a brush was jiggled out of place and had reset itself. Nope. Two point nine trips later the battery got so low that the idle speed dipped and surged when I put on my turn signal. I was able to coax just enough power out of the motor, put the car in neutral, and coast into the driveway as the motor died up the road. What had happened is this: after you battery gets below a certain critically-low output, there isn't enough current to light up the warning light bulb. By putting a low-resistance bulb in, it'll light up a little longer than the other bulbs, but that's it. So, if your alternator light doesn't light up, be sure your battery is fully-charged. If no, charge the battery and check the regulator brushes. If it is, check the bulb.
Good luck. Don't let an untrained idiot that doesn't care about your car try to change your alternator.
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