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Classic/Antique Car Repair/Generator Idiot Light

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Expert: - 9/24/2008


Question
I have a 1969 Chevy el Camino with the generator idiot light illuminating.  I have replaced the alternator and voltage regulator, but the lamp is still lit.  Voltage readings at battery terminals are as follows:  engine off - 12+ Vdc, engine running at idle - 13+ Vdc, engine running at 2000RPM - 15+ vdc. The accessory belt is tight and battery does not run down overnight; voltage pretty constant.  Any ideas?  Your input would be greatly appreciated.
drew

Answer
There a a diode in the alternator that controls this light and the charge rate for the alternator. It is called the diode trio and most of the time when the idiot light stays on but the alternator is charging it is the diode trio that is defective. Also make sure that the ground between the alternator and the regulator is in good contact.
Brad

Classic/Antique Car Repair

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Brad Sears

Expertise

All automotive including antique and collectible. However if the car has been modified I can only answer in general terms and maybe get you pointed in the right direction.

Experience

Automotive tech instructor. Syndicated auto columnist 1970's though the early 1990's. Syndicated auto radio talk show, Ask Brad About cars, CBS Radio 70's through 90's TV Show "Last Chance Garage" 1980's PBS-TV syndicated. Auto instructor for the following companies: Fram Autolyte Holly Carter AMF Ford Motor University Of Conn Blue Hills Technical School Sugar River Technical Center Grew up in a family garage in Needham Mass and turned wrenches from the age of 14.

Publications
Manchester Union Leader, Nashua Telegraph, Motor Service Magazine, Yankee Magazine, Popular Mechanics (Saturday Mechanic early 80's), Los Angeles Times, New York Times, and lots more.

Education/Credentials
More than I care to remember. Basically Franklin Technical Institute in Boston, Northeastern University, Fitchburg State Teachers College, Tufts University, and a lot of factory schools along the way.

Awards and Honors
Moto Award winner. And much more.

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