hello,
i have a 1991 f150. 302cid, automatic, lariat, sclb. im at a loss as to what has happened. i was driving down the road at night and all of a sudden the stereo cut out and squelched and the headlights went out. i immediatly stopped. the headlights will not turn back on but the bulbs arent blown. no fuse is blown. i replaced the battery and headlight switch. the alternator was checked and is fine. when the headlight switch is on the dash, brake, and parking lights come on but there is a sound like something short circuiting. the chime fades and pops also. the stereo will only turn on sometimes and just shows the time. everything else works fine as far as i know. any ideas?

 

sounds like some thing shorted out. you need a test light. That way you can turn the headlight switch on an see if you have power at the bulb, if not you just start working your way back through the wiring looking for power, once you find it you know the problem is in between where you are and where you were.

 

since the truck has obd1 and eec is it possible to hookup a diagnostic computer?

 

yeah but i doubt that is gonna help with a headlight problem

 

i also have a 91 check the fuse again because the radio interior lights head lights and speed control are run off the same fuse if its a short the fuse will be blown, look at the diagram the fuse should be a 25, just take it out and put a 30, ohh and check and see if the cigerete lighter is working

 

all the fuses are good. further inspection shows a flare like burn on the module that connects to the headlight switch. an audible short can be heard somewhere towards the front of the motor toward the bottom and near the frame and is only heard when battery cables are connected and the headlight switch is plugged in

 

I would check the head light switch, Ive had them go bad before.