I. Basic Parameters

OE: 21N8-42050; DC 24V; Rated 120A High-Power Preheat Relay; Master Solenoid Switch for Diesel Engine Glow Plug Preheat Systems

Structure: Features two heavy-duty copper terminals + one single-pin black waterproof connector; includes a metal mounting bracket; designed for direct plug-and-play installation with the original vehicle harness—no wiring modification required.

Aliases: Heater Relay, Glow Plug Relay, Intake Air Heater Relay

Interchangeable Part Numbers: 21E7-3012, 36860-72010/72011; physically identical and universally interchangeable.

II. Compatible Models (Key Hyundai Excavators + Wheel Loaders + Forklifts)

Excavators

R140LC-7A/9, R140W-7/9, R160LC-7/9, R210-7, R215-7, R225-7, R305-7, R330-9 (All models equipped with Cummins engines)

Wheel Loaders

HL730-7A/9, HL740-7A/9, HL757-7A/9, HL940 (Hyundai Wheel Loaders)

Forklifts

Hyundai 100D-7, 110D-7E, 135D-7, 160D-7 (Heavy-Duty Diesel Forklifts)

III. Wiring Definitions

Two Large Bolts: One terminal connects to the 24V positive (+) battery post; the other terminal connects to the power supply for the entire glow plug assembly.

Single Black Wire (Small Gauge): ECU temperature control + ignition control signal line; the vehicle's computer automatically regulates the preheating duration based on the ambient temperature.

IV. Symptoms of Failure

Difficulty starting the engine in cold weather (cold start issues); emission of excessive white smoke during startup; preheat indicator light fails to illuminate.

Internal Contact Sticking/Welding: Glow plugs remain continuously energized (stuck "ON"); results in battery drain and/or burnout/damage to the glow plugs.

Preheat indicator light remains constantly illuminated (does not turn off); preheat fuse blows frequently.