Relay

5 pin relay (Part 90017800), a compact 12 volt electrical relay used in the wiring and control systems of Ottawa yard trucks and terminal tractors. It’s listed in as a “relay, SPDT (single-pole double-throw) 40 A miniature 12 V”, meaning it is a high current control relay that switches power between circuits based on a low current control signal. Relays like this are common in starter, lighting, horn, accessory, and control logic circuits in heavy duty truck electrical systems. functions like an electrical traffic controller in the yard truck’s wiring system. When a command (such as turning on a key switch, activating a light switch, or engaging an accessory) is given, the low current signal energizes the relay coil. This, in turn, closes or opens the internal contacts to allow a higher current flow to the load.