Join Date: May 2011
Location: Frederick MD.
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Follow the wire coming off the relay and you will find it run to the x pipe or "spider" coming right off the turbo. The heater has one wire from the relay and a ground wire going to it.
You can try and key on the truck and check for voltage at the heater itself. Often the heater will burn up though. And I forget what the ambient temp had to be but I think it has to be below freezing for the intake heater to even come on. Some people delete the heater anyway.
Another way to test it would be to run a KOEO test, which will cycle the relay.