I think if you look at the www.serpent-usa.com site, it will list a switch.

Also, I think Michael's mechanic (or UB... can't remember) mentioned on the mytsn 950 thread that Michael uses a switch that can only be gotten from a German website (non RC one). Can't recall the website but it was mentioned that Michael uses that switch on all of his 1/8th scale car.

Else, I think KO also makes an on off switch. Expensive and I think the unit itself kinda drains off some power if I'm not mistaken.