Installing a Manual Cooling Fan Control Switch
 

I want to install a manual switch to control the primary cooling fan on my 89. Where is the best place to run the wires through the firewall and easiest place to install the switch?

I put my switches in the glove box.

Anyplace you can find on the firewall close to the center is a good place, try to find a rubber plug and stick a awl thru it and then fish the wire in with a coat hanger.

I would suggest you have the memcal reprogrammed for lower fan temps. Forgetting to turn on the fan can result in big problems, and leaving it on when it is no longer needed can be counterproductive.

Here's a better way to do it. I just installed this on my '91, and it works PERFECTLY! Before installing, my Vette would run up to close to 240 when idling in traffic. Now it turns on the fans REALLY close to the advertised 195 degrees and keeps on going till just a hair below 180, where the fans shut down. Wish I'd known about it sooner.

ECKLER's Corvette Low Temperature Cooling Fan Kit, 195º, GMP, 1984-1995
1991 CHEVROLET CORVETTE STANDARD
Part #: 40416

You only need one wire through firewall or tap into terminal C1 at ECM, the other side of switch goes to ground.
I have my antenna switch beside ALDL connector, might be a good place for your fan switch.

Pin C1 completes a ground when its programmed values are meet. See my site under my username, or install the above mentioned kit. The ecm shuts the fans off at 35 mph.