Thanks Mexicow. I will go back and drudge through it. I did some testing with my meter, not a light bulb but same principal, and haven't found a draw.
Obviously the diode can conduct current when bad, otherwise a bad one would not let power go from battery to panel at night. Did I answer my own question, or am I missing something? If I can go buy a new diode then that is an easy thing to do, and easy to wire in, much easier than what Im about to do.
Anyone have experience with possible culprits? A short? wouldn't that cause a fire or smoke?
There is really nothing in my RV that uses power except the charge controller, everything is on a switch that disconnects the power circuit when in off (as opposed to electronic things that always have power to the power switch). The charge controller is a very small one.
I appreciate any suggestions as I go through the long process of dismantling the electrical system.
It is custom made, so I can't answer make and model, but the circuit breaker came out of a 1970 Winnie, and includes a converter/charger. Circuit breaker is for AC, but Charger is connected to the batt. The DC circuit is 6 fused switches that I keep off. Water pump is a 7th separate switch that is always off. Generator is directly connected (not connected for this project), Frige and solar panel used to be directly connected (fused) to batt, but now on the 6-switch panel. Charge controller still directly connected, but testing showed no current between it and battery.
thanks
notes:
when I say battery goes dead overnight, that is after the initial drain when the RV sat for a few weeks alone. I could charge the batteries back to 12v, but they were in poor shape by then and would lose voltage more quickly than a normal good batter would. Autozone would charge them and swear they were good, and they would hold charge free standing, put them back in coach and they were dead (11.5 volts or less) the next day.