Hobbs Meter
There are two basic methods for wiring an electric engine Mour Meter. The most common is to wire the Positive side of the meter to the "run" or "on" terminal of the ignition switch. The disadvantage to this installation is that the meter will run anytime the switch is in the "on" position, even if the engine is not running.The preferred method is to wire the Positive side of the hour meter through a normally-open engine oil pressure switch. When the engine starts and the oil pressure reaches the set point of the switch, the contacts will close turning on the hour meter. This method gives a true indication of engine run time.In both cases, the "other" wire is Negative.