My '86 F150 4x4, 5.0l EFI was fitted with A/C by an aftermarket application, although i've seen many trucks like it fitted with the same style of A/C. There is a silver fan motor relay mounted on the firewall above the blower motor. My problem is that i've only got high speed on the fan. The other speeds don't work. The switch and fan motor are brand new. Does anyone know where I can buy this relay or does anyone know the part number. Ford doesn't seem to know as they say it's aftermarket. The other parts vendors tell me to go to Ford. What gives?

 

Most likely it is not the relay you are talking about. All speeds except high speed use a resistor to limit the current through the motor. It sounds like your resistor is bad.

 

what you want to do is find the relay, and pull it out and visibly inspect it for corrosion, my 87 bronco fullsize had the same prob, lo, and med would nt work, pulled the relay out, and the rust ate away at the relay.

 

I agree with Kioolt, it's the blower resistor assembly...

 

im sorry i was meaning the resistor assy as well, located by the blower motor, get it from ford.....i think i paid like $15 for mine