The EASIEST way is to use the spring loaded electrical gizzie.
Go to a competent Chevy/GMC (I stress competent, here!!!) parts person, and have them look up the contact set for a 1993 GMC Safari pass side sliding door contact set. There are two parts, with two separate part numbers required, to do this. I saved the boxes for mine, and will try to dig them out later to post the part numbers.
Anyway, these have two contacts on them...and with NO metal trimming, will fit into the spaces available most satisfactorily.
You can also use this contact set to support two circuits...just get a thin braided flexible ground strap and screw mount into the body jamb and left rear cargo door jamb to provide a proper ground to the door shell. It folds into the door jamb when the door is closed. Of course, the light won't function when the door is open, which is of no consequence.
Steve