[theresa2000]

While driving, the headlights go out; they do not come back on for hours in some cases. Hazards/ flashers still work.

Also happened once during the day with no headlights on ... simultaneously, motor surged/ lost power briefly as headlights go out (if they were ON). Also I heard "clicking" noise during power loss/ surge. Engine power loss was very short-lived.

When power surges (and headlights go out if ON), the radio, outside digital temp, dash lights, and power windows all fail. After driving a while with flashers one night, the Check Engine light, then Air Bag Light came on.

So far this has happened 3 times, all in the last month - twice at night on dark mountain roads, once at 11 a.m. on a mountain road. Temp approximately 38 degrees F or less each time, and, each time, as it got warmer outside (lower altitude in all cases,) all problems vanished including warning dash lights.

During first episode we noticed headlamp switch was very hot. We replaced switch; old one was burned-looking. New switch stays cool but same issue has occurred twice since replacing switch.

 

[ImperialCrown]

Welcome to Allpar. I would start by looking for bad connections/corrosion under the hood under the fuse/relay (IPM) box by the battery.
With the headlamps on, try gently wiggling wires to see if you get a flicker or any reaction from that.
With a helper, try wiggling wires under the dash. Gently move the ign key towards 'off' and 'start' to see if you can reproduce the radio and power windows failing.
The ign switch position wouldn't affect the headlamps. You may have more than one problem here.
The headlamp switch is a 5 volt 'sense' switch for the BCM (body control module-can store fault codes), which buses the light request information to the FCM (front control module-can store fault codes) mounted on the underhood fuse/relay box.
If the 'ck eng' and Airbag lights came on, a fault code may be stored in the PCM (powertrain control module) and ACM (airbag control module) to help determine the failure area.
The hazard flashers are on a separate circuit and are probably not affected.
The IPM accessory relay may have been the one clicking as radio and power windows, etc. go through that relay. It keeps the accessories on for a few minutes after turning the key off until you open the door.
For further diagnosis, you may want wiring diagrams for wire colors and routing and at least see what fault codes may be stored. You may need the assistance of a more advanced scan tool than just an engine code reader for this. The better the diagnosis, the less time and frustration can be spent finding the culprit.
Some diagrams here: http://www.google.com/search?q=2001+chrysler+minivan+wiring+diagrams&hl=en&client=safari&tbo=u&rls=en&tbm=isch&source=univ&sa=X&ei=qzXgUJ_lC8ew0AG1_oAo&ved=0CD0QsAQ&biw=1429&bih=768