This relay switches electrical loads in the cab of the host tractor, controlling functions such as lighting, HVAC fans, or wiper motors. It is a standard four- or five-pin Bosch-style relay that mounts in a dedicated socket or fuse box. A relay that fails internally will cause the connected circuit to remain off or stay permanently on, depending on the failure mode. Bosch manufactures this component to match the original contact rating and coil resistance, so it switches cleanly without voltage drop across the contacts. When replacing, verify the socket wiring orientation matches the relay pinout before inserting.