Hi guys

i have a 89 gta 5.7 with dual fans. The fans kick on like there suppose to, but i would like to have the choice to control both manually. I am interested in installing a manual fan switch. However i would also like for my car to operate as gm intended. What is the easiest way to add a manual fan switch, for BOTH fans? I have been studying the chilton, & chevy thunder wiring diagrams. I would like to tap into the wire as close to the ecm as possible. Is C1, or E8 the wires I need to tap? any help would be great. btw I don't even see C1 on my chilton diagram.

 

I have no idea what pin at the ECM you would need, but you'd want to find the connection for the A/C wire that controls the fans - the second fan only comes on with the A/C as I understand it, and therefore BOTH fans would operate if the system was "fooled" into thinking (with your switch) that the A/C was on, whether or not it actually is on. I know on my single fan 1992 car, there is a green/white wire running to the A/C compressor that actuates my single fan whenever the A/C is actually on.

Hope that helps some.

 

Since you have two relays that controls two fans, you'd need a Dual-Pole (DPST) switch that can turn on both relays, by grounding them. You'd need to ground E8 and D11, separately.

I would advise against grounding the A/C input on the ECM (B8) because that would make the ECM increase the RPMs for the A/C to kick in.

Hope this helps.
Lou

 

Dual fan control that DOES NOT disable factory fan setup. It works great...

https://www.thirdgen.org/forums/elec...en-3647-a.html

 

Agreed
The ECM grounds the relays to engage the fans. T into the ECM wires (should be dk grn/wht stripe) and ground them via switch and you should work