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| Detail | Specification |
| Part Number | 540 (TUNG-SOL Corp.) |
| Part Type | Vintage Heavy-Duty Thermal Turn Signal Flasher |
| Voltage | 12V |
| Terminals | 2-Pin (Standard Flasher Post Style, typically marked 'X' and 'L') |
| Load Type | Thermal Flasher (Compatible with Incandescent bulbs only) |
| Lamp Load Capacity | Heavy-Duty, Variable Load. Typically rated for $3$ to $6$ incandescent lamps, often used when a standard 552 flasher may experience "running on" or a slow flash rate due to increased lamp resistance/load (e.g., when adding lamps or on larger trucks/vans). |
| Application Notes | Used for the Turn Signal function on vehicles where a robust 2-pin 12V flasher is required. This part often cross-references to the more common aftermarket 552 specification flasher, but with a heavier-duty rating. |
| Make | Representative Models (Turn Signal Function) | Representative Years |
| General Motors (GM) | C/K Series Pickups, G-Series Vans, Impala, Chevelle, Camaro, Nova | ~1956–1981 |
| Ford | F-Series Pickups, Econoline Vans, Mustang, Galaxie, Fairlane | ~1950s–1980s |
| Chrysler / Mopar | Dodge Trucks (D Series), Plymouth, Dodge, Chrysler Passenger Cars | ~1950s–1980s |
| AMC / Jeep | Gremlin, Hornet, Javelin, CJ Series Trucks/SUVs | ~1960s–1980s |
