I've got a 12v feed to the rad switch so when it opens this activates the relay. I have a new 12v fused feed to 30 and 87 to the positive terminal of fan. New earths from fan and relay back to battery. I also have an override switch with a feed into 86 to activate the fan manually if needed.

In summary 30 is fused 12v from battery
87 is feed to fan positive
86 is switched 12v from rad switch and/or override switch to trigger relay
85 is earth to battery

You also need to connect earth from fan. Some may do it differently but this works for me.

Hope this helps.