Do the headlights and heater fan go out completely? Have you noticed other circuits having problems at the same time, or other indicators doing odd things? If so, how do they behave? And does it keep running OK some of the time?
We need some detail to be able to figure the likely issue. Could be something opening up or something shorting; so some further info will help.
If you have any idea how read a wiring diagram here is yours in this list of downloadabe links; it wil be good to use this so we can all work from the same page.
http://www.mymopar.com/index.php?pid=28
