E36 Fan Switch in E30

[lennon]

I want to use the E36 M42 radiator fan switch in an E30. It is 80C low speed, 88C high speed, vs. 91/99 for the E30/E36 325i. This is for a swap, the car has no mechanical fan, and an aftermarket electric pusher fan wired into stock wiring.

Here's the problem: The E36 switches GND on at the fan relays, my E30 (1988 model) is wired to switch POWER to the fan relays. The E36 switch recieves its GND on the same pin as the E30 switch recieves PWR. I think the other two terminals (high and low speed) are reversed between E30 and E36, but that's a secondary problem now.

I ASSumed the switch wouldn't care whether it's switching PWR or GND, so I tried the switch but it does not turn the fan on. Did I fry the switch? I can let the car warm up completely, and begin to overheat (200F+ according to known-working VDO gauge), and the switch never closes to either terminal (as tested with a multimeter).

Help me out.


Edit: I forgot to add, the fan wiring is good. If i jumper the terminals of the fan switch connector, the high and low speeds both work.

[vpilarrt]

I have one (an E36 switch) on my '91 318is which has the same circuit as the rest of the E30s and it works OK. You have to make sure your cooling system is well bled as the switch is high in the radiator. I would remove the switch and test it in a pan of water on the stove while monitoring the water temp.

[lennon]

Thanks for the reply. I was thinking the same thing, because of it's placement. I bled the system, but I will try again.

Any other ideas anyone?

[nando]

your post makes no sense. the E36 M42 switch definitely works with the stock wiring. it doesn't matter if the E36 switches +12v or ground, it's just a switch. it doesn't have a polarity.

if it's not working there's something wrong with the car's wiring, a fuse, a relay, or the fan itself. or as mentioned, possibly the car isn't bled correctly.

[lennon]

your post makes no sense.

How does it not make sense? I think I spelled it out pretty clearly.

if it's not working there's something wrong with the car's wiring, a fuse, a relay, or the fan itself.

I said in my original post that the fan works just fine on both speeds when the switch connector is jumpered with a wire.

Thanks for the helpful post dude... You basically just repeated what I already knew/said in my first post.

Anyway, I bled the system more and got the switch to close, hopefully I got it bled completely, and the switch will be dependable.