Lovely piece of crap! Come on, now...just because it ain't a vette!
What is going on, could have easily already been there. Or, putting the harness in, a wire could have been pinched. THAT can happen to anybody.
Is this the same car that had a little smoke, from the dash? If so, find it, you've probably found the problem.
I'd hate for someone to go through, what I did, many years ago. First car, 63 Sport Fury ragtop, that I had for a handful of years. Wanting to be the cool hot-rodder, decided to go with a trunk-mounted battery. Wire this, wire that, good to go.
Then, one day, dang top up, 65 miles an hour on the freeway, left hand lane, cabin filled with acrid white smoke, so thick, I had to get my head out the window to even see. Got the car to the side, jumped out and popped open the hood. Had the pleasure, of watching every wire in the engine compartment burn...just like a fuse.
Lucky it didn't catch on fire. Had to have every wire in the car replaced.
Hot wire to ground.