94 Astro van electrical problems

Never disconnect the battery to see if the alternator is bad. If it is good, the voltage could go very high and damage the electrical systems in the car and even wipe out the light bulbs. Instead, check the voltage AT THE BATTERY with a good voltmeter with a charged battery, the engine idling, headlights on, and the heater fan running. You should measure 13.5 to 14.5 volts. If the voltage is low, the alternator is weak.

You should see a constant 14 volt charge on you meter if the alternator is good, if it's bad your charge will go down little by little. Take it off and take it in to have it checked

If you do not want to check this yourself, bring your car to the local auto parts store if possible and they will usually check an alternator for free.