Quick I did post the wrong year info 94, vs your 84. You are correct it is a positive fed from switch to motor through resister. Those years had some Very complicated wiring set ups including being fed through the AC switch as well. Some just by passed the the trucks wire diagram and rewired their own setup in using the trucks fan switch to operate the blower. I know, not what you want to hear. But in can be fixed the right way as well. But checking a diagram out there appears to be a lot of possible failure spots. For a 84 truck, I would rewire it to make it as easy as I could.