This factory-style modification allows you to toggle the auxiliary fan to high speed when the AC is on, improving AC performance at idle.

The E30 comes with a fog lamp switch, which in some markets is a double switch. By using the alternate switch (part number 61311380312) and adding two connectors to the existing plug, you can use the extra button to control the auxiliary fan. This method can also be applied to install a switch on the climate control panel (which uses switches of the same size). However, in this case, all four climate control panel positions were already in use (hazard lights, audio fader, window circuit breaker, and defroster).

In 1987 and before models, the radiator temperature switch is on the driver’s side, so the two-conductor cable can run through the factory firewall grommet along with the existing wiring to reach the switch. In 1988 and later models, the radiator temperature switch is on the passenger side, requiring the cable to be routed accordingly within the engine bay.