How to cheaply build a latching relay system to disable a circuit until power is cycled?
simulate this circuit &ndash; Schematic created using CircuitLab
Probably easiest to use a SPDT relay with the NC contact for your sensor and the NO contact wired back into the relay coil.  D1 depends on your coil rating, the 4148 is just the standard one the schematic editor puts in.  V1 is an ignition controlled supply that can handle your sensor.
Edit: if it's important that the sensor only have power if you are in reverse, use a DPDT relay and hook up the reverse light and sensor to the other pole.