Also. you may have a broken or shorted wire, usually inside the rubber boot between the door and body. I had the same issue. My son, a mechanic, unhooked the wiring inside the door and pulled the wiring through to inside the cab and soldered/shrink tube repaired the break. Problem solved. You can buy shrink tubing with sealant inside that is a good investment or you can squirt some dielectric grease inside to help prevent corrosion in the future. I'm sure some will have a problem with using the dielectric grease but since the wiring is inside a sealed rubber piece it shouldn't be an issue. The wires are prone to breaking since it flexes every time you open/close door and the wires get brittle with age.
I though relay from searching online but after testing found it was fine. Son worked on lots of different makes of vehicles over the years and was the "go to guy" for wiring problems at BMW, Cadillac, etc. and first thing he said was if the relay tested okay then go straight to wires inside rubber boot because of age of vehicle. He came over and did the repair in about 20-30 minutes total. Would have taken me hours but turns out this is a very common problem with our trucks/Blazers/'Burbs with electric windows/locks. Good luck.
