Thanks for all the input. I thought it was stock because it is a perfect hole with no chewed edges or anything. It is about 1" in diamerer. I'm not sure how you would feed a cable up into the space between the inner ceiling and outer roof. I';; try to get a pic tomarrow. I'm in the process of grinding all the paint off the cab so it is bare metal now. I ground the plug right out.
Thanks again
ivor