I was wondering if anyone knew what the factory used to undercoat the floorpan/body on the inside of a 1990 pickup?
There's a top coat the same color as the duco, but when you look inside the various cavities and on the floorpan you can see this tan-colored undercoat.

I need to remove it from a threaded hole so I can use it as a good ground connection.
I'm not sure if it's a normal paint, so I don't think paint stripper will work. The threaded hole is only 8g metric, so there's no room to get a steel brush in there

Thanks,
David. :beach:

 

I seem to remember the "paint " you are talking about on my 93 pickup. I think the best thing to use would be a tap. This would cut through the "paint" to bare metal for a good ground. If this didn't work, maybe use a blow torch on low to burn the threads clean.

 

Thanks for the ideas Highland. I had thought about using a tap, but I'd have to drill out the thread and re-tap it with something bigger. It's basically just a nut that's been tack-welded to the body, so there's not too much material to spare.

I had a look at some of the other bolts that are used as ground points and noticed a couple of them still had this undercoat paint on the threads. When I ran a bolt into the hole and tested the continuity with a multimeter it looks like it will make a sufficient ground after all.