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Sounds like someone mounted a first generation Hobbs electric hour meter on the H. I doubt it’s original - the only IHC “factory” hour meter I’m aware on the letter series tractors is an odometer-style mechanical revolution counter, mounted sideways on the right side of the engine front cover. John Deere however did use the clock type electric meter – I believe it was standard equipment on the model R… Internally the hourmeter is essentially an electric solenoid-wound, balance wheel escapement type clock mechanism similar to 50’s era automobile dashboard clock, only calibrated to read in hours, tens and thousands. Applying voltage to the hourmeter causes the solenoid to wind a small clockwork mainspring. The clock mechanism then runs for approx 2 - 3 minutes. Then as the mainspring is almost completely unwound, a set of contacts close and cause the solenoid re-wind the mainspring. The cycle repeats and the meter continues to run as long as voltage is applied to the hourmeter terminals. ---- If your H has distributor ignition easiest place to wire the hour meter is to the switched (coil) side of the ignition switch, or the ign switch side of the coil primary. However if the tractor has magneto ignition you’ll need an alternative means to run the hourmeter. Probably the easiest is to add a “normally open” oil pressure switch - ie. one that’s contacts CLOSE upon sensing oil pressure. Then run a series circuit from a battery source (eg. hot terminal on the light switch) to the pressure switch and finally to the hourmeter.
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