2 Power Sources To 1 Radiator Fan

hi. My Car Radiator Fan is all stock.. I have a Dakota Digital Electronic Fan Controller as a stand alone system.. It has its own temperature sensor wired to the transmission cooler lines... The wiring of the dakota system i understand... The question is.... How can i tie both system into 1 single radiator fan.. My stock system is dual fan. How can i wire the dakota system into one of the fan and prevent power to flow from the dakota current/power to the ECU which controls the stock system... I I couldn't add an additional fan to the system because theres no room for it.. Once the dakota system reaches a certain temperature i would like the fan to turn on and it will turn off automatically.. The system would be a Y configuration in some sort... The bottom of the Y is the Radiator Fan and the 2 top of the Y is the Car ECU Radiator system and the Dakota Digital Fan controller. Martin

Does the OEM system switch power or ground to turn the fan on? One will be present all the time, the other only when above the certain temperature. Which one is constant, Power or Ground?Let's Go Brandon Brown. Congratulations on your first Xfinity Series Win. LGBFJB

hi, The OEM system switches the red wire positive.. The black wire is always negative... I checked it yesterday.. The negative didnt chance polarity.. The red doesnt have any current, it shows up like a red wire but once the fan turn on, it shows positive...

Cut the red wire or find a place you can interrupt it and then take the wire end/side that goes to the existing electrical fan to terminal 30 of a proper sized relay and then the wire off of the car to terminal 87a of that same relay. Now, wire terminal 87 to a fused power source and then this leaves just terminals 85 and 86 of the relay to be setup to work with the output of the Dakota Digital controller. If the Dakota Digital controller sends out a ground signal, then connect that to terminal 85 and then connect terminal 86 to terminal 87 (which is a fused 12V). If the controller outputs a positive 12v signal then connect that to terminal 86 and then connect terminal 85 to ground. Since terminals 30 and 87a are normally closed, when the factory setup wants to turn the fan on it can but then when you want the Dakota controller to activate the fan the controller will send a signal to the relay and then connect the fan to the battery or a source of power. Personally I would wire terminal 87 to the battery because you could have a backfeed situation of the fan being de-powered and feeding back voltage to an ignition 12V source and possibly powering up the ignition system until the fan slows down enough and cannot provide enough power. Jim1968 Chevy II Nova Garage Find 2012

1973 Nova Custom

1974 Spirit of America Nova

1973 Nova Pro-Street