I bought a switch today for my radiator fans. How do I wire it to the fan switch on the engine? Can I leave the wire plugged into the fan switch on the passenger side of my L98, and splice into that wire? Also, the switch has three prongs on the back. The instructons say one is for the ground, another goes to the device which is the fan in this case, and the other goes to a 12V source. Do I need to hook up the 12 volt part? Thanks for any info! Matt

 

You're trying to turn the fan on more often than the sensor asks it to? Then you need to run a separate wire from your manual switch to the hot side of your fan, otherwise you'll just be turning the juice on and off to the sensor. And yes, you need to bring 12V to the hot side of your switch.
Why do you want to do this? Mine's a motor-driven fan, but I was planning to change over so I could move the radiator around a little. Is the sensor not keeping it cool enough?

 

I just hate how high the temp climbs before the fans kick on. I might try something else first like a lower temp fan switch. Matt

 

how high is it going?

 

Lockdude is incorrect about the fan switch wiring. You DON'T use 12 volts. You are correct, simply leave the wire on the fan switch and splice into it. The spliced wire goes to one end of the manual switch, the other end of the manual switch tie it to a good ground. You are simply manually doing what the fan switch does. The fan switch in the block grounds internally through it's threads to the block providing a ground for the fan relay which handles the current the fan or fans require. Never run 12 volts for a fan motor through a switch, one the wire size you need for the current makes it impractical for underdash use and second most switches are not designed to handle an average current of anywhere from 6-20 amps. With most stock dual fan setups if you turn on the aux fan first BOTH fans will run. The ECM detects if the aux comes on before the primary and goes to a default mode turning on the primary as well. One thing I strongly recommend is to replace BOTH fan relays. The stock relays suffered from a design problem which caused intermittent operation of the fans thus overheating problems. GMSPO and NAPA supply a different internal design relay which is much more reliable. GM # 14089936, or NAPA AR-279. many guys think that going to a manual switch to correct fan operation will solve a problem. Truth is in most cases, if the relay(s) are funky it does nothing. Also inspect the relay connectors for signs of discoloration and overheating of the female connectors. Repair as needed otherwise a new relay will fail prematurely if the socket has too much resistance.

 

Oops!