Both fans are coming on at the same time....there is no wire connected to the switch on the passenger side head...could that be the reason? Or is it wired so that both come on at the same time, any advice would be great. And also, around what temp does the primary fan come on? 89 iroc z...5.7 TPI

 

Depending on how long you have owned the car and what has been done to it they could have been wired that way by a previous owner, someone wired fans on my 87 that way, spliced into power for one fan to run the second instead of fixing it correctly... just a thought

 

I'm thinking that has to been it...because like I mentioned, the plug that goes on the sensor that tells the second fan to turn on, is unplugged

 

The fan switch is a part prone to failure from a lousy design. Instead of replacing it they may have taken the wire from it and joined it to the wire from the ECM that turns on the primary fan at or near the fan relay. Trace back to your fan relays and see if an extra wire is spliced in somewhere

 

[I]Here are the schematics from a 91 camaro w/AC.
Both fans will come on if there is AC pressure. Otherwise they're pretty independent. Primary fan is controlled through the ECM. And trhe secondary fan needs AC or coolant switch, and is not ECM controlled.

 

The 90-92 730 is different from the 165 as far as the pinout goes. The wiring should be the same fashion. Secondary with head fan switch or ac request

 

If that fan switch wire is grounded it will turn on both fans

 

Since the wire only leads to the secondary fan relay I find it highly improbable
that that will happen