I also had problems with vibration "bouncing" the contacts in my 1/2 A Pylon Racers.
I solved the problem by substituting a stereo type jack in place of the monaural ones we had been using. Simply wire it so the two sets of contacts are in parallel with each other. This solved the problem for me and the engines we're using turn over 30 grand. The plug that turns off the system is also wired to act as the charge plug.