anyone with a m90 ecu wire up a fan overide switch ? i have the wiring diagram for the relay and color code but dont want to double up on pin 86 on the relay if it feeds back to the ecu? yes ive tried the mfg. i want fan to run after engines off .
Do you just want to add a manual switch that you can turn on with the car off? If so, there are a few ways to do it.
1. You can just put a diode on the line coming from the ECU to the relay coil to prevent feedback if you want to add the switch to the same coil pin. If your relay doesn't have a quenching diode you may want to add one.
2. You can also add in another couple relays, one normally open and one normally closed. You would wire your switch to the coil on both. On the normally opened one, you would jumper the coil feed to one side of the contacts. On the normally closed, you would wire your ECU output to the fan relay coil to the contacts. Both new relay output contacts would land on your fan relay coil. Under normal conditions with your manual switch off, the ECU output would feed the fan relay coil. When you flip the override switch, the normally closed relay would open and disconnect your ECU output from the fan relay and connect your switch output.
3. Another way would be to add a duplicate fan relay. Feed one with your switch and the other with the ECU.
If that's not what you want let me know and I'll see if I can come up with something else.
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