Abstract: An electronic control unit suitable for a motorcycle provides diagnostic support, tachometer drive and warning lamp drive all multiplexed onto one pin and driven by a single driver circuit. In a diagnostics mode, the pin is connected to diagnostic equipment. When a diagnostic test has been completed, a tachometer drive signal is output on the pin, the drive signal having a duty cycle set high enough to illuminate the warning lamp if a fault condition is detected by on-board sensors. By combining multiple functions onto a single pin with a single driver circuit, the cost of implementing an engine control unit may be reduced compared with existing arrangements which require separate pins and drivers for each function.