Do you have the wiring diagram you used to set this up with the Volvo relay?
I just wired it like the picture on the relay. The input power wire comes straight from the positive battery terminal with a 30amp inline fuse.
Did you use the BMW temp sensor that some have suggested or did you go another route?
When I was carbureted, I simply installed a toggle switch on the dash to send the (low power) ground signal to activate the relay and turn on the fans. Now that I have my FiTech system, I use its fan signal ground output to control the relay.