> Anyone have any ideas?
> Bad ground or door latches?
No, your problem is too _much_ ground.
The interior-light circuit is hot at all times; the lights go on whenever it finds a ground, such as via a pin switch in one of the doors, or the 20-second timer module, or (no one has mentioned this one) the headlamp switch, when you rotate the **** fully counterclockwise.
> How to trouble shoot?
Check your door pin switches and your headlamp switch, for starters. If they're all okay, it sounds like you'll need to find and unplug the timer module. If that doesn't kill it either, you'll have to start looking for a wire somewhere that'* shorted to ground.