Do you mean the lights get dim while you're driving? That's a sign the generator isn't working. Have the charging system professionally load-tested. If the generator is only developing exactly one third of its rating, it has one bad diode. That will not be enough current to meet the electrical system's demands under all conditions so the battery will have to supply the rest. If there is no output at all, check the operation of the "Battery" warning light on the dash. That is the turn-on circuit for the generator. If that light doesn't turn on when you turn on the ignition switch, the generator might be okay, but it's not turning on.
Finally, measure the battery voltage with the engine running. It must be between 13.75 and 14.75 volts. If it stays near 12.6 volts or less, measure the voltage on the generator's output terminal. If it is a lot higher, there's a break in the circuit between there and the battery.
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Monday, February 25th, 2013 AT 12:28 AM