benny0983 Posted February 17, 2013 Share Posted February 17, 2013 hello everyone i have a question i work for a trash company and im trying to bypass the ecm to turn the fan hub off at temp i have drawn out the wiring diogram using a relay and factory selonoid for the fan hub that was the easy part the hard part is im the third or fourth person to try to fix the fan allways on driver says its driving him nuts because its so loud in the cab of his truck i am using a new temp sensor screwed in to one of the ports on the thermostat housing the biggest issue is using the temp sensor to ground the relay but it wont throw the relay notes its a mr688s mack the wire harness for the fan hub selonoid is missing i have looked at sister trucks and its gone and all the plugs are the same two prong so finding the actual one is kinda hard if its even still there thanks for any help Quote Link to comment https://www.bigmacktrucks.com/topic/30008-coolant-sensor/ Share on other sites More sharing options...
staxx Posted February 17, 2013 Share Posted February 17, 2013 What year is the truck ? the fan solinoid wire has a extention harness comes off the back of the head drivers side rite below very last intake manifold bolt , most likely wire extension harness between back of head there and solinoid is cut somewhere . Quote Link to comment https://www.bigmacktrucks.com/topic/30008-coolant-sensor/#findComment-165423 Share on other sites More sharing options...
Challenger Posted February 18, 2013 Share Posted February 18, 2013 Sounds like an Aset AI engine if there are ports in the Tstat housing. Just adding that there are 2 coolant temp sensors. One that sticks out of the back of the water manifold that points to the rear of the engine, this one is for VMAC III. The second one is in the side of the water manifold towards the back and points out towards the tire, this one is for the temp gauge. Quote Link to comment https://www.bigmacktrucks.com/topic/30008-coolant-sensor/#findComment-165460 Share on other sites More sharing options...
staxx Posted February 18, 2013 Share Posted February 18, 2013 Your a/c high pressure sensor and cool temp are what turns your fan on or off grounded through the engine ecu Quote Link to comment https://www.bigmacktrucks.com/topic/30008-coolant-sensor/#findComment-165485 Share on other sites More sharing options...
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