91 Caravan electrical problems

I have a 91 Grand Caravan SE that is doing some strange things lately. Yesterday the wife turned on the rear defroster and the following stopped working: ammeter, rear defroster, radio, door locks, power mirrors, interior lights and the warning tones for headlights on or keys in ignition. I checked the voltage at the battery with the engine running and got a reading of 11 volts. If anyone could help with this I would be very grateful!!!!!

Take your altnetor off and have it checked for free.You should get 13.5 volts across battery running.And check grounds 3 on fwd mopars