Fitment: Replacement for FM350 FM352 FM500 FM502 FM600 2000XL MM500/502 series Mighty Mule GTO | Function: It is composed of a tachometer and a limit switch to prevent the door arm from falling off. The counter board can calculate the opening distance of the door opener to help you solve the problem that the door cannot be opened | Material: the counter plate surface is coated with a layer of gel, which can reduce the influence of fog, rain, snow and humidity | Determine the fault location: if the main boom fails, you will hear 3 beeps, and if the auxiliary boom fails, you will hear 4 beeps. You need to check and replace the circuit board in time | Note: Please keep it sealed during installation to avoid short circuit of circuit board caused by water ingress.