I use two separate circuits with their own relays and fuses... no reliability problems with it at all (had it like this for 2 years now), it allows me to use any switches I like, I don't have to run 20 amp hot wires through the firewall and all over the place, and it's simple and safe.

I have not done this yet but if I do I will use relays for more juice. The wiring on a standard Single Pole Double Throw (SPDT) relay is as follows:

85 - Ground
86 - Switched +12 Volts this wire is the one you put you switch inline.

30 - constant +12 volts direct from battery (fused)
87a - nothing cap off
87 - connect to fans to turn them on.

Now if the fans are negative switching - Meaning that it takes a negative trigger to turn them on simply wire 30 to a good ground (no fuse needed). The rest of the wireing remains the same.

944sracer wrote:


Mine are similar, but I also have a small wire going from the fused constant +12 volts to 86, then put the switch inline between 85 and ground. This allows me to run the fans after a race with the engine and ignition off, plus it's super easy to find a suitable ground inside the car to wire the switch too.

Another thought is that if your relay has both 87 and 87a terminals, I like to run the constant +12 volts to 87 instead of 30... that way you have one less terminal that's hot most of the time and could ground out on something. It's not a big deal, since you should be insulating this stuff anyway, but it's just as easy to wire as the other way.

I just cut the harness and run my own wires from the fans (reusing the factory connector) to the battery, inline fuses and a switch in the car. I did this to avoid all the stock wiring to the fans. I had an issue with them not coming on right at the track and this was the easist way to ensure they are working.

My are direct the battery are hot when ever the kill switch is in the on-position.