On the
fireblades RC51 forum there are plenty of information for both the SP1 and SP2. There is a great SP1 solution that works without a switch.
The SP2 fans are controled by the ECU not by a thermal switch as in the SP1.
The signal from the ECU goes to the tail to a relay that turnes the fans on. It is better to tap on the input wire ground of the relay than the higher Amp. output cirquit where an adequate switch is necessary.
There is a black wire going to the relay that when is grounded it turns the fans on.
Although on an other thread here someone brought up the point of where the fuse would blow if the fans have already been turned on and automatically and you flip the switch.