Alternator light
Thread Starter
Instructor
Joined: Sep 2006
Posts: 100
Likes: 0
From: MISSOULA MONTANA
Alternator light
Been playing with a pesky little electrical problem. My alternator light glows continually. Alt. output is good-apx 60 amps. Battery checks out good. always starts strong. light glows a little brighter at idle and dims as rpms go up,but never out. A mechanic in our shop said, sounds like it could be a bad ground. Can only find two grounds in the AIM man. Neg batt cable & engine block to frame. I am sure there must be more. But where???
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
How it works is the start.
When you turn on the key, power flows from the battery, thru the light ,to the field of the alt. As engine speed increases, the output voltage increases, and the field current is supplied from the output of the diode trio. When the voltage on these two circuits are about the same, the light goes out.
Your dim light is a result of the diff in voltages of these two circuits.
1)Battery undervoltage.
2)Bad gauge fuse
3)Bad alternator
4)Resistance in the light circuit. IE, bad plug in alt, bad connection on the circuit board, corroded light socket,etc.
Good luck. It just takes time to find it. If you tested the batt and alt, it's #4
Your dim light is a result of the diff in voltages of these two circuits.
1)Battery undervoltage.
2)Bad gauge fuse
3)Bad alternator
4)Resistance in the light circuit. IE, bad plug in alt, bad connection on the circuit board, corroded light socket,etc.
Good luck. It just takes time to find it. If you tested the batt and alt, it's #4
Intermediate
Joined: Aug 2006
Posts: 34
Likes: 0
From: Raleigh NC
Check the diodes in the alternator. Car parts stores like advance or carquest should have one in the store. My alternator had a shot diode and gave me this exact problem. It was even more annoying because it was screwing with my choke relay. What year though?
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
Yep. That will do it too. On early 80 cars with electronic gauges, this will also make them go wacko.
