i have never used a failsafe on any of my robots with electrolise in them, the 15 and 30 amp microprocessor controled ones have an adequate failsafe with in there design. remember a failsafe eg fs1 in the event of loosing radio signal will output a signal to the controllers still, and assuming you are only using one failsafe, with the radio off you now have a signal from the failsafe mixing with what ever the Rx is picking up in the way of noise. so your speedos are now getting a signal good enough to not allow them to failsafe and what ever noise will let them go nuts.

try them with out the failsafe, i think youll find it works ok then. or if you must, use two.