Can anyone advise on a battery drain overnight-2002 Chev Silverado 1500 LT
symptoms: Towhaul button coming on by itself-everything turned off at night-morning-tow haul on-battery drained.

1) BCM has been reprogrammed at dealer-I replaced the BCM with a used one after first dealer recommended a new BCM because old one was 'sticking'.
2) Problem of towhaul coming on reappeared after two days of trouble free operation
3) Checked wiring from shifter switch-orange wire is tow haul circuit wire-will expose column today to check connection again
4) Tow haul is wired into BCM control so I don't think I can pull its fuse independently

I suspect grounding problem somewhere in steering column or under dash-a kelsey trailer light and brake control was installed so I cut power to it just as an experiment-BCM is turning on towhaul on its own so I doubt it is the trailer lights circuit but I'm open to any advice.

Anyone have similar issues? The battery drain was investigated now at one licensed shop and two dealers shops-I have the job now to fix this and its a bit humbling that a dealer spent 6 hours and didn't use a scanner tool immediately-they repeated the licensed shops steps checking charging circuit etc.

There was a GM service bulletin pointing to BCM reprogramming for 2002 Silverado battery draining symptoms-this has been done.

Thank you