OK some I'm rebuilding the motor in my 89 Formula 350 TPI. Both the connector for the Coolant Fan switch and the Knock sensor are identical and I'm not sure which one goes to which, they're only about 8" apart so the wire length is not helping me. I originally noticed this when I first bought the car and was replacing the starter... Looked like a previous owner had been in there looking for something and screwed with stuff
Anyone know a way to figure this out before the motor goes back in... Already replaced both pigtails because the originals heat cracked into dust. One is black wire the other is white wire.
All else fails I'll wait till the motor and all electronics are hooked back up, ground each one and see which one turns on the fan...

 

According to AustinThridGen.org, knock sensor is white wire (87 5.0/5.7 and 89 5.0 diagram but not?!? in the 5.7 diagram, left lower) and the black wire is the fan relay trigger (lower right in the diagrams).

 

Found that just after I posted this... It looks like that was the way it was hooked up before.. Black wire had more heat damage

Thanks!!

 

To confirm your analysis: If you ground the fan switch wire the fan will turn on. If you ground the KS wire, nothing happens.

Assuming the key is on and fans/relays work, of course.

I had to figure out the same thing on a butchered 87 once without the aid of a wiring diagram. Had me scratching my head for a while, too.