Transmission Cooler/Cooler lines

I think you need to put another hole in you transmission oil pan......
If you added a temp probe in the pan you could run the fan by temperature. If you are racing down the track, heading down the return road or setting in the pits.

If you tied it to a battery feed(fused of course) then the fan would just run when it need to and you wouldn't have to do or thing about thing during the race. Then just add a two way toggle switch so that one way you can turn it on manually and the other way to can disconnect connection.........just so you can have complete control of system.

This is what i do with my water pump and radiator cooling fans and fuel pump.
My water pump turns on at 160 degrees and my radiator fan turn on at 180 and off at 160. but i can turn then on manually if i want as well.

EDIT that's a 3 way switch on/off/on"temp controlled"