The 1804A-12 (P/N 535-0127) is a 12 VDC engine start solenoid for diesel fire pump applications. When the controller calls for a crank cycle, the solenoid closes the high-current circuit between the battery bank and the starter motor, carrying the heavy cranking load that the controller's pilot contacts cannot switch directly.
A failing start solenoid is one of the most common reasons a diesel fire pump engine will not crank. Typical symptoms include a click with no cranking, intermittent starts from one battery bank but not the other, or burned contacts after years of weekly test cycles. If your engine cranks unreliably, test the solenoid before condemning the starter motor itself.
This solenoid suits diesel fire pump engines with 12-volt starting systems; a 24 VDC version (1804A-24) is also available. Cybertronic Controls is veteran-owned and ships from Hammond, Louisiana — call 985-351-5681 to confirm fitment for your engine.