This is part 2 of a 2 part series on how to install and wire Spal Slim Fans. Part 1 looked at creating brackets and mounting the fans on the radiator.
Now that the fans are installed on the radiator, it's time to think about how to do the wiring. For those of you that don't know how the stock fans work, the passenger side fan is the primary fan that goes on when the coolant reaches a certain temperature. The driver side fan only goes on when you have the A/C on. Since the Spal fans are supposed to be a performance upgrade, it'd be pretty lame and pointless to have one of them turn on only when you have the A/C on. I want to have both of them on at the same time so I can get maximum cooling. There used to be a vfaq on vfaq.com that shows you how to jump the cooling fan relay to get both fans to turn on at the same time, but as you can see, the link for 1Gs is dead. The 2G link still works, but I'm too stupid and lazy to figure out what all those wiring diagrams mean and apply them to 1G cars. (Update Dec 2015: it appears both vfaq links are dead now)
The passenger side fan is pretty easy, I just cut the stock wiring and connected it to the Spal fan. Black goes to black, and the other color is positive. The positive wire on the 12" fan was red and the one on the 11" fan was blue, so just remember black is ground and the other one is positive. Now the 12" fan works just like the stock primary fan -- it turns on when the coolant reaches a certain temperature.
The driver side fan is a little more involving since you can't just connect it to the original harness (unless you are retarded and only want it on when the A/C is on). There are probably tons of different ways you can wire the driver side fan, but what you DON'T want to do is simply splice into the same power source as the passenger side fan. I asked Ty at RRE about this and his answer was yes, you will fry the wire if you have the same wire powering both fans. I came up with 2 ways to do it and both involve using a relay (got mine from Radio Shack).
One way to do it would be to splice terminal 85 or 86 of the relay into the power for the passenger side fan and power the relay directly from the battery, then use the relay to power the driver side fan using power from the battery (that'd be terminal 30 and 87 on the relay). This way, when the passenger side fan turns on, the relay turns "on" and so does the driver side fan.
Another way to do it would be to find some other "on" power source for the relay and have a cockpit mounted switch for it. I chose to do it this way so I can control when the driver side fan goes on. A plus about doing it this way is if the coolant temp sensor ever dies, you can still turn the driver side fan on. I just spliced a wire into the power for my gauges and added a switch to it, then ran that wire through the firewall to terminal 85 (or 86) of the relay that powers the driver side fan.
Either way, remember to splice a fuse somewhere between the battery and the fan. I just used an inline fuse holder with 30 amp fuse (just like the one I used for the fuel pump rewire).
All done! I was too lazy to take pictures of the wiring by the time I got this far, but I'll add them someday (please use your imagination for now :P).
