I did a search and found a lot of info but it seems to aply to the older models. I have a 91 z28 that the blower motor works intermintently. You hit a bump and it works and hit another and it quits. I checked the gray/black connector with brown wire behind the heater controls and looked fine. while i was there i checked all the other possible switches and stuff and everything looked fine nothing looked burnt. right now its working fine. Last night I stopped to put fuel in it and it didnt work half way home. I cant seem to find that gray/black connector under the hood by the evap.case. There is one by the coil and connents to the coil but that cant be it. This thing is driving me nuts. Any info would be greatly appricated. Not sure what to check and didnt want to replace everything under the hood. I thinking of starting with the blower motor maybe the brushes are wearing out in the old one. thanks

 

also I forgot to metion my doesnt have a ground wire like the older models but it has a two prong power/ground connector. if there is a different ground I cant seem to find it. Thanks

 

I would check the relay before the blower motor. Its right next to the blower motor connected to the evap. case. That would be my first thing then start looking at the wiring. The relay is in the engine bay though not in the dash.

 

Yup' Probably the relay.

It's a cheap part that's easy to replace - good place to start looking ! I had a S10 Blazer that acted EXACTLY as you describe. In the coldest winter months it really sucked when I needed to open the hood just so I could Tap on that relay with my finger to get the system blowing heat again !