Aftermarket automatic fan switch/relay

I need an aftermarket fan switch/relay/trigger for my KW with a 3406B mechanical CAT. The fan works if you hit the switch on the dash but since the truck originally had an ECM controlled engine it does not work as there is nothing to trigger the fan.

Is there a specific KW harness or parts kit that I can put in or can I just use one of the many aftermarket ones sold at the auto parts store? I'm leaning towards the 2nd route. The switch in the dash is wired thru a relay. If I go that route where do I want the probe, in the radiator or what specific part of the engine?

Also what temp should I use as the trigger temp for fan ON and what temp for fan OFF?

Thanks

 

Thanks!

Ended up ordering a Proform kit # 69598

 

Getting ready to install the kit and hit a couple snags.

First the kit uses a negative signal to trigger the fan and the stock KW wiring has the fan triggered with a positive signal. So I'll need to wire in a second relay that's triggered negative and supplies a positive...not sure what the exact terminology is.

2ND is I gotta drain the coolant and adapt the probe. Any idea what size the sensor ports are on the front of the head?

 

Here's the photos. First are ports on top of the head and the second is on the side , ahead of the thermostat housing.