Your best chance of finding a door for your Celebrity is in a local wrecking yard.
You could try Craigs List for a car someone is parting out.
You could also try Ebay. I have not ever seen one there but it could happen.
You can find a fuse block diagram in either a Chilton manual, a Haynes manual or a factory service manual.
I find no reference to anti-lock brakes in my factory service manual or other reference works so I assume that they were not available in 1986.
You can find the wiring diagrams for a Chevy Celebrity in either a factory service manual or either a Chilton or Haynes manual.
Looking in my factory service manual for a 1989 Chevy Celebrity I found no reference to an accessory relay.
Any Chevy Celebrity sedan or station wagon front door from 1982 to 1989 should fit and work correctly. Sedan back doors will not work on a station wagon, station wagon rear doors wont work on a sedan. The window frames are slightly different. I would look for them in a wrecking yard.
what type of engine do you have?? V6
On google images type "door handle diagram Chevy C1500"
junk yard
Check in either a factory service manual, Chilton manual or Haynes manual. There you will find illustrations of the markings on the sprockets and their alignment for which ever engine your car has.
The adjustments are preset at the factory. If the door is sagging it may need new hinge pins and bushings. IF you have changed doors and the hinge pins and bushings are good the adjustments are on the door post behind the dash or the kick panel on the bottom. The hinges are commonly tack welded in place and the welds have to be broken. It is a royal pain in the neck to get to the adjustments. If you have a factory service manual or a Chilton or Haynes manual you will find better help there. GOOD LUCK
Prices tend to vary with suppliers, there does not seem to be a standard price. When I need parts for my Chevy Celebrity I survey the local sources and buy the best deal I find.
Looking in my 1989 Chevy Celebrity manual I find a park relay inside the wiper motor but no reference to an external wiper relay. There is a fuse on the fuse block.