a simple test light with an alligator clip to earth is very handy for working out which wires are hot and when they are ON/OFF.

if you havent got one, you can rig one up using a bulb, bulb holder and pigtail with wires.

The other good reason to go the switched relay path is that if you decide to run a temp sensor to switch the fan on and off then it will be easy to wire in a "normally open" temp switch to the earth circuit and run the + signal wire straight to battery voltage.
This will then mean that the fan only kicks in when the temp sensor/switch reaches it's preset temp and earth. You can choose different temperature sensor/switches to match what temp you want to stay at.

The relay isnt actually connected to anything at the moment. Who ever put the fan in the car just left it screwed next to the radiator. I didn't realize it wasn't hooked up at first as the + and negative wires where running to the fan behind the relay so I thought it was ok. So there is a relay there but its just cosmetic at the moment. The positve lead of the fan is straight to the coil with a fuse and the negative is to the battery.

This is what I plan to do as it doesn't need to be on all the time especially for cold weather starts.

This is a nice simple diagram I just Googled of how to set it up when you're ready. The opposite of how I said (it's switching the positive via thermal switch rather than earth but same result)-

heres a nice thermal switch you can get from jay car for $1 or $2.



and the links 1 2

I like that thermo switch... i cant work out how it fits? is it on a T piece?

sorry I just hit the 2nd link... all clear now.

yeah all good. Im still not sure if it would be affecting coil output a lot but I will wire it off my alternator this weekend to be sure and put a switch on at a later date. Thanks for all the advice so far.