I can try. I’m just a backyard “hack” with electronics so I’m sure there are other ways, perhaps simpler, to advance a digital hr meter and it probably depends on the meter. The modern digital meter does not advance simply with a 12v supply. It needs an actual tach signal from the engine. I called the manufacture of the tach/hr meter and asked their tech, what signal shape and voltage the hr meter was looking for.
My circuit does not exactly mimic what I was told but it was close enough to work.
The schematic in the picture is a basic “timer” or “clock” circuit. The heart of it is an IC chip called a “555 timer” and is readily available at Radio Shack or any other electronics supply store. C1, C2, C3, R1, and R2 are Capacitors and Resisters used to set the output of the timer to any particular frequency. The tables just indicate the values of the capacitors and resisters to achieve a frequency (simulated rpm of the engine). I used the values as shown on the schematic. The speaker was there just so I could tell it was working. I assemble the circuit on an electronics “bread board” also available at Radio Shack.
The circuit will run on a 12 volt power supply and output approximately the correct signal amplitude.
Once you get the hr meter running, set an alarm clock for yourself to turn it off. They don’t go backwards. S
1995 ProStar 190