1995 Chevrolet S-10 Having Charging problems

Tiny
EGO_SUM_ASW
  • MEMBER
  • 1995 CHEVROLET S-10
  • MANUAL
  • 100,000 MILES
I got this truck a couple days ago and the previous owner said that the battery was bad but I think that the alternator may be bad or the wiring is discontinuous. There are two wires coming from the main post of the alternator. That connect to the battery black and red which both have continuity. Then there were also two wires coming from the alternator plug one was a dead end and the other led to the wiring harness. I'm trying to figure out what may be the problem. Voltage at the battery when running is less than what it should be. Any help would be appreciated.
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Friday, March 28th, 2014 AT 2:19 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
What specifically do you have for battery voltage with the engine running? What kind of problem are you trying to solve?

GM has had a real big problem with their generators since the '87 model year. Due to their design, they produce huge voltage spikes that can damage the internal diodes and voltage regulator and interfere with computer sensor signals. When you need to replace the generator, to reduce the high number of repeat failures, replace the battery at the same time unless it's less than about two years old. As they age they lose their ability to dampen and absorb those spikes.

Besides testing for proper charging voltage at the battery, which should be between 13.75 and 14.75 volts, you need a professional load tester to test for maximum output current. If you have a failed diode, all you'll be able to get is exactly one third of the generator's rated current. 30 amps from the common 90 amps generator isn't enough to run the entire electrical system under all conditions.
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Friday, March 28th, 2014 AT 5:31 PM
Tiny
EGO_SUM_ASW
  • MEMBER
We had the alternator tested and turns out it was bad. Thank you!
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Saturday, March 29th, 2014 AT 1:06 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. "Bad" can mean a lot of different things. Without knowing what was wrong with it or how much current it could produce, be safe and replace the battery too to avoid the all-too-common repeat generator failure. If you don't, it's common to go through four to six replacement generators in the life of the vehicle.
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Saturday, March 29th, 2014 AT 7:52 PM
Tiny
EGO_SUM_ASW
  • MEMBER
Now were having problems again. We replaced both the battery and the alternator and it's still not charging. All that I can think of is bad wiring perhaps.
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Saturday, March 29th, 2014 AT 8:11 PM
Tiny
CARADIODOC
  • EXPERT
I need details to analyze. Measure the voltage on the bolted-on output terminal with the engine off and with it running. Does the "battery" light on the dash turn on when the ignition switch is turned on? If not, unplug the small connector from the generator, then use a piece of wire to ground the terminal for the small brown wire. That should make the "battery" light turn on. If it doesn't, there's a break in that circuit.
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Monday, March 31st, 2014 AT 11:06 AM

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