I've been trying to figure this out for some time now. Still not sure what to make of this, as I'm no good with wires.
I bought a 200 degree fan switch from Jet, and went in to find the fan switch, only to find that it has been replaced with some sort of plug. The person that owned the car before me, I know he rewired the car so that the fan turns on when the vents inside the car are turned on. Or something like that, if I remember right. When I got the car the fan was only manually turned on, so it never came on with temp. Right after I got the car a family member of mine took it upon himself to rewire it so that it turns on with temperature, and for the most part it does now. All I can remember is him replacing the fan relay and temp sensor at the front of the intake manifold, though. I'm confused as to how the fan comes on at a certain temp with no fan switch. I want to install this lower temp switch for the upcoming summer months. Anyone know where I should start?

 

If I remember correct the 85 has several temp sensors. Primary fan operation is from the computer though, using the engine temp sensor. I'd guess he rewired to trigger the relay from the computer. Secondary fan is a separate circuit from its own sensor. You'd need to find a wiring diagram and get into it pretty deep to figure this out.

 

Its single fan, not dual. But I think you're right about the computer controlled thing. I pulled the plug looking thing out of the usual fan switch position and it turns out it actually is a fan switch, but it looks like someone broke everything distinguishing about it off. I also found that I guess in 85 the fan relay is located on the exact opposite side of the others. Its usually on the drivers side firewall, but on mine its in the corner near the passenger side fender. I spliced into one of the green/white wires going into the relay and connected it to the fan switch, and it seems to be working the way it should. The temp gauge isnt reading anything further than 190 or so anymore.