On the rear of an alternator is a small wiring harness. This harness, over time, can become brittle and break. It may seem a horrible task to repair as the harness is very long and splits off in several places. A small trick is to purchase just the end section (pigtail) from your local parts store or even a salvage yard and replace just that part. This can save you days of aggravation, tracing wires and trying to match exactly what the manufacturer did.
Disconnect the negative terminal of your vehicle's battery.
Open the hood of your car and locate the alternator. It will be near the front of the engine compartment on a rear-wheel drive vehicle and on the left side on a front-wheel drive vehicle.
Remove the harness from the alternator. The harness is removed by pressing the locking tab on the harness and pulling it out.
Clip all of the wires going into the harness.
Strip about 1/2 inch of the wire cover off of the wire on the wires in the car and the new harness using the wire stripper.
Twist the bare wires together making certain to match the wire colors together. Solder the ends of the wires together using the soldering iron and solder. Protect the connection by taping the bare wires with electrical tape.
Plug the new harness into the alternator.
Reconnect the negative terminal to your battery and turn your vehicle on. Verify proper operation by putting the multimeter terminals on the battery while your vehicle is running. The volts should be between 13.5 and 14.5 volts, if there is a reading that is more or less, it is a clear indication that there are additional problems.
