Installing a/c on a truck that didn't come with it...

Okay. I've got a customer who dropped off a 1990 MM and a 1987 D-50. The 87 has a rockin body but is carbureted and nobody took care of it. The 90 has been chopped(dancing bed and such). But has a good 4g64. Customer wants good 4g64 put into 87, which had the G63B. Get the under dash harness swapped, fuel tank wiring swapped, and instrument cluster swapped along with pcm. Cool. Put dash back in. Customer says that they now want working ac in the truck. Drops off some lines, the little "A/C" switch, and the compressor/bracket. Neither of these trucks had ac to begin with. I know I still need a condenser, accumulator and evaporator core, complete with thermostat. The wiring is what gets me. Looked at a wiring diagram for an 89 (which I assume is the same) and it has confused the heck outta me. Never wired an ac from scratch. I know the compressor is case grounded, and the power must go through the pressure switch before getting to the compressor. That's about it. Any ideas?

Hi and welcome to mightyram. First up - can't swap the 4G64 with the G63B. The 4G64 is a wide block engine and would require a matching transmission swap (great as you have the whole truck as a donor by the sounds of it) The A/C's are pretty much wired up all the same. There should be provisions in the 4G64 wiring harness for the A/C so that will save you chopping into or adding anything to the harness to hook it up. We have wiring and service manuals here on the site but you have to be a donator to access them IIRC. You can add an aftermarket condenser core with a dryer (you can get them cheap off ebay, but it may take some assing around with hoses/lines to connect it and some hand fabricated mounts to anchor it up front)