I've got a similar problem, actually a couple of problems. My battery will discharge in about 3 days if I don't keep a tender on it. I did notice that the "volt meter" always shows the voltage of the battery, key on and key off.
My other problem is not enough shop space or time to get under the dash to see how my father wired it up. (It's a popular aftermarket wiring harness).


Another quality post.
Real Trucks Rattle
HELP! The Paranoids are after me!