Was moving the new project out of the driveway...hit the rear defroster switch and headlights dimmed and the amp meter took a nose dive.Shut it off and everything went back to normal...Bad Switch or rear defroster wiring grounding out somewhere? Any ideas?

 

Don't poor water on them gremlins they multiply.

 

I would lead toward the bad grounding being the issue. I would even more so think that especially if you could recreate the issue. Good Luck!!

 

Now I would think either shorted motor or grounded hot in the wiring.

Bad ground the motor would probably just not work. Now dipping amps / dimming lights tells me that voltage is leaking to an already solid ground.

 

X2 bust out the wiring diagrams and multimeter
your grounding out somewhere

 

I like to use the "divide and conquer" method. Unplug the motor at the door and then turn on the switch. Amps stay the same / no dimming, it's the motor. Other wise just as tanner said, look at a diagram, go to a connector towards the middle, break it, and see if the condition still exists. Keep working your way back until it clears and then with the meter you can start testing the section beyond where you broke it for a short.