1998 Dodge Caravan dash light

You have an intermittent problem and the testing has to be done while it is occurring. There's no way to know that with it on a test bench. Normally alternators need to be tested on the vehicle to be accurate but in this case you likely have worn brushes. You can verify that by measuring the two voltages on the two smaller wires on the back of the alternator. Those have to be taken while the engine is running. One will have full battery voltage. The other one must have less but not 0 volts. Typically you'll find between 4 and 11 volts.

My bet is when the light turns on you will find 0 volts on the second wire. If you have 12 volts on the first one that is proof the brushes are worn. The assembly costs about ten bucks. I've replaced them on '95 and older Caravans without removing the alternator from the engine. I don't know if you can do that on a '96 and newer model.