installed aftermarket pioneer radio, shuts its self off when moving

my radio works just fine if the vehicle is stationary, however if i move forward or backward the whole unit seems to lose power. the whole screen goes black no noise or anything from it, however if i stop, say at a stop light or in a parking lot it comes back on until i move again. for the life of me i cant figure out what the problem is. ive checked the wiring and connection and all seems to be good. i am at a loss.