The generator light stays on until I rev it

September 1, 2016 | By Staff


I have a 1961 Chevy bubbletop Impala with a 283 V-8 that I converted from a generator to an internally regulated alternator. I followed the instructions to the letter (blue wire to generator lamp, white wire to battery, and took the external regulator out of the circuit).

The alternator puts out about 14.4 volts at idle. But ever since the changeover, there have been many occasions when I start the car and the generator light stays on until I rev the engine. Then it goes out. Do I need to reduce the pulley diameter on the alternator to increase its speed at idle or do you have some other solution to remedy this problem? Other than this issue, the alternator seems to work just fine. Thanks for any help.


What you are experiencing is a common occurrence with the type of one-wire alternator you have installed. I installed a similar one on my 1955 Chevrolet and the charge light glows red until you rev the engine and energize it. If it bothers you, going to a smaller alternator pulley or switching to a CS series Delco alternator will remedy the problem.

The self-exciting one-wire alternator has a special voltage regulator that doesn’t need a wire from the ignition to activate it. This would be one that only requires a wire connected to the battery terminal. Inside, there is a voltage regulator that controls alternator output and contains circuitry that uses the residual magnetism in the alternator’s rotor fields to determine when to turn the alternator on and off.

A standard Delco alternator will not automatically shut off the charging light without an ignition activation wire. The regulator works by sensing the RPM the alternator is turning, and when it gets to a certain speed the voltage regulator kicks in. Typically when you start the vehicle and rev the motor slightly the alternator starts charging. However, with the CS series Delco alternator equipped with the self-exciting voltage regulator you do not need to rev the engine.

That’s because the CS series alternator with a self-exciting voltage regulator will give you faster alternator voltage. This type of alternator is commonly used on custom cars, trucks, and tractors, and other non-standard applications when ease of alternator wiring is important. In choosing one-wire alternators consider whether you mind revving your motor slightly to get the alternator to turn on. If doing so bothers you, it would be best to install the CS series type alternator. Or you can find and install a slightly smaller pulley on the standard Delco alternator you have.