The reversing light switch is mounted on the outside of the gearbox housing. You need to remove it in the following way. Place the lever in neutral. Raise and support the vehicle securely. Disconnect electrical connectors. Remove the switch and washer by twisting them away from the housing.
In the removed state, the switch can be easily checked with a tester by measuring its resistance. In the normal state, there should be a gap between the contacts of the switch. When you press a button (or plunger) switch, the resistance between the contacts must be zero.
When assembling, always replace the sealing washer between the circuit breaker and the housing. It not only prevents oil leakage, but also sets the length of the protrusion of the switch inside the box. Tighten the switch with a tightening torque of 25 Nm. Connect the electrical wiring and lower the machine to the ground.