Dimmer switch gets locked on

This is one I've never ran across before so I thought I would post it to see if anybody has come across this. My friend/customer has a '93 Roadmaster with the security system transmitter etc. on all the newer cars. His battery went dead the other day and it was changed (4yrs. old) under warranty at the local Murray's Auto Discount store. I don't think it was bad, and the guy never charged it up and did a load test etc. (another story here). We put in a new battery and checked the alternator/regulator for output and everything seemed o.k.

The next day the battery was dead. I failed to test for draw the first day because I forgot my test light. After re-charging the battery I noticed the dimmer switch was locked on. He said he never touched it. O.K. well maybe so. Now it gets weird. After re-charging and setting the alarm system the dimmer switch got locked on again. I played with the switch by putting it all the way up and locking/un-locking the switch and could hear a movement(not fully up or down) in the power door lock system. Could there be a jump in voltage here somewhere? The door locks shouldn't move when you touch the dimmer? I feel maybe when he locks/ un-locks the car with the transmitter it's setting the dimmer switch to lock. I know this sounds impossible but I've seen it happen. Where does the problem exist? Is the dimmer all one part with the light switch/twilight sentineal? Any ideas? Thanks