- Mar 2, 2015
- 6,822
- 5,859
- 203
With the bmw sensor you could use two relays and a diode. The low speed would ground the low speed relay by itself. The high speed fan relay would have two wires coming off the trigger....the one going to the low speed would have a diode in it. That way when low speed is triggered the ground path can't go to the high relay... but on high it would allow flow to both.