I just purchased a 1972 barth (25'limited?) it has a progressive dynamics PD 710 converter.When plugged in my 12v system does not work. I SHOOK the coach and the 12v lights would blink on and off. Then it rained and some of the 12v lights turned on. there is a switch back near generator with a glass fuse that has a on and off switch,when the switch is off the 12v works not the 110v and vice versa. I found two (of the probably many) grounds ,cleaned and then replaced with no changes . Any help would be greatly appreciated.

jay - I had a similar type of problem with the 12v lights down the right side of my rig. They would work once in a while, but not usually.
I got under the rv with my trusty spray can of electronic cleaner (you can buy this at any electric supply) and sprayed absolutely everything that looked like a wiring connection (and a few that didn't). It worked! Everything is turing off and on correctly at the moment.
It's at least a good place to start and use it on your switch also.

Godd luck - Tigger

Thanks tigger I will crawl under the beast and spray it all over like you said. Thanks again.