I have an 88 jeep wagoneer limited. Problem is while riding down the road I can turn the defroster on and the engine starts stumbling real bad and will cut off.... turn everything off and it will fire back up and run fine, turn the defroster back on it does it again. then sometimes i turn it on and there is no problem. a/c compressor is not hooked up so its not that putting a strain on the motor. please help me!!!! thanks jason

 

I'd check for a short in the blower motor wiring.

 

This is an odd electrical issue. My first guess is that one or more of the grounds between the body/engine/battery may be going bad. This is causing current to go the wrong path. This is creating a voltages in places they are not supposed and disrupting sensors indications to the computer and the computer ability to drive actuators.

Start with cleaning all of the ground strap connections you can find under the hood. The two I can remember are by the battery, at the back of the head.

You may also need to open inside the cabin and clean up ground connections there as well. Especially by the computer and the tie heater fan.

Also look through the fuses and make sure they are all in tight and clean.

 

Is anything vacuum controlled? If so possible vacuum leak?

 

You've got a short somewhere. Find a wiring diagram...

Grounds are at the dipstick tube and firewall to cyl head BTW.