If a vehicle idles up and down the lights dim with idle when it is in gear battery light comes on would that be an alternator problem?

It's possible that the problem could be with the alternator, but it is not the only possible cause. Here are some other things that could be causing the problem:

* Battery: The battery could be old and weak, or it could have a loose connection.

* Starter: The starter could be drawing too much power from the battery when it engages.

* Voltage regulator: The voltage regulator controls the amount of voltage that is supplied to the battery. If the voltage regulator is faulty, it could be providing too much or too little voltage, which could cause the battery light to come on and the lights to dim.

* Alternator: The alternator is the part of the car that generates electricity. If the alternator is not working properly, it could be providing too little electricity to the battery, which could cause the battery light to come on and the lights to dim.

To identify the source of the problem, it is recommended to have the vehicle tested by a qualified mechanic. They will be able to diagnose the problem and recommend the appropriate repairs.