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Yukon Cornelius

Charge warning lights burn dim at idle and got out at 2k RPM

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My son's barn find 86 Brat. Has multiple issues we've been working through. Currently were working on the charging system. The alternator is charging at 14v at idle but the charge warning light burn dim. EGR, brake, charge, and stop lamp. These light go out at near 2k RPM. I'm pulling the alternator out now to check the brushes. Any ideas fellas?

MVIMG_20200518_201528.jpg

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Every time I have seen this it was one of the alternator brushes. 

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Check with a meter in AC voltage at the alternator. Should be under 1V, very close to zero. If it as a external regulator, check at the regular instead. Forget what year that went to integrated regulators.

Edited by Ionstorm66

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Next would be bad ground somewhere. Simple test is to stick a jumper cable from battery negative to the alternator, and one from alternator to chassis.

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The battery indicator shows if the voltage potential is higher at the battery OR the alternator. So a poor connection, bad alt, or bad battery could do it. Generally though if the light goes out at higher rpm it's the alt. May have just been light corrosion on the slip rings that will wear off as it runs. 

GD

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Meh, cleaned the contacts and reassembled. Still does the same thing. Not one of the more pressing issues with the vehicle as its charging 14v during operation. And the list of issues is long. I'll come back to it and report a repair when I find it. It's most likely just diode issues. But, not bad enough to fail the diode test on my tester. Moving on to rear brake hardware and fuel level sensor

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