How can I figure out which one is the problem?
Oh yeah...how can I fix it also ?

 

Try gluing a penny (with silicone) on the inside, back of your sliding door so that it will come into contact with your your auto door lock switch button. The switch is probably not being depressed enough to shut your lights off and the DOOR AJAR warning (dings) off.

 

Usually it one of the sliding side doors getting slammed shut to many times!!!!
Look at them..... I'll bet one is stuck in.... You can pull it out as a temp fix, but you'll need to replace it!!

 

You can also go out when it's dark and look real close at the lights when you open the doors one at a time.....
one door will not make the lights a little brighter..... That's the door with the failing switch