My heater fan in my 93 4x4 4cyl quit working lately and I'm not quite sure yet what's wrong with it. Any recommendations on tracking down the problem? Can I run wires to it directly from the battery and just use a simple On/OFF switch to run it at full speed when necessary until I figure out the problem in the factory harness? I'm pretty sure the fan will still work. The problem would come and go before and I could get the fan to kick on by flicking the outside air/circulation lever back and forth a few times until the fan would come on.

I'm sick of rolling my window down while I drive to keep the windshield clear of fog.

 

i don't know what that fan pulls, but i'd make sure to put a fuse inline as well as make sure your switch is capable of the amperage.

 

Maybe use a relay? I have a couple laying around.