Thanks to all for their advice/suggestions. The truck has been re-wired and changed over to 12V with an alternator. Since I do not know how to verify whether or not it's the alternator causing the leakage I will pull fuses, one at a time and see if I come up with the solution. Alan, I have not checked your diode installation but will do so shortly and see if it's something I can do.

Thanks again, Don