Hour meter power source
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Hour meter power source
I want to put an hour meter in the truck for the new engine. I don’t want to power the meter when the key is in RUN but the engine is actually off. Would tapping into the oil pressure sending unit or the tach signal wire be a good source without causing those circuits to act weird? Any other thoughts for a power source? As a side note: I converted the oil gauge from an “idiot light” to a real gauge so it has a real sending unit and not a switch.
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Gas - 351W
Thanks. That’s the circuit I’ll use.
Thanks. That’s the circuit I’ll use.
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I eventually got around to this over the summer for the new engine. I used an extension with two ports so I can use the oil pressure sending unit for the gauge and switch to run the engine hour meter.
Logistics Pro
Joined: Nov 2013
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From: Mojave, Ca
I would not tie anything into the ignition system of these trucks. The PIP and ICMs are finicky and even unmodified systems have problems; don't **** it off by adding another load to it.
Real industrial equipment and airplanes use an oil pressure switch to run the hobbs meter. I suggest you follow their example.
If you wanna be slick, you can add a relay to your current oil-pressure switch. When the oil pressure is low, it'll turn on the "low oil pressure light". When the oil pressure is high, it'll turn on the hobbs meter.
Real industrial equipment and airplanes use an oil pressure switch to run the hobbs meter. I suggest you follow their example.
If you wanna be slick, you can add a relay to your current oil-pressure switch. When the oil pressure is low, it'll turn on the "low oil pressure light". When the oil pressure is high, it'll turn on the hobbs meter.
Last edited by Prototypemech; Nov 16, 2025 at 05:18 PM.
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Laughing Gas
Joined: Jul 2009
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From: NE Ohio
Just for a point - Aircraft have 'Tach time' and 'Hobbs time' . This can translate to cars/trucks where they count 'Idle Time' like newer police cars so sitting at idle at a speed trap/or while writing a ticket counts counts as one measure, and high-speed pursuit counts as another for wear/tear on the engine. Using an oil pressure switch would count as Hobbs Time.The difference between Hobbs and Tach time is the following:
- Hobbs Time:
- The time from when the engine starts to when the engine stops.
- Tach Time:
- At cruise RPM, tach time counts like a standard clock.
- At an RPM less than cruise, tach time counts slower than a standard clock.
- At an RPM more than cruise, tach time counts faster than a standard clock.
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Real industrial equipment and airplanes use an oil pressure switch to run the hobbs meter. I suggest you follow their example.
If you wanna be slick, you can add a relay to your current oil-pressure switch. When the oil pressure is low, it'll turn on the "low oil pressure light". When the oil pressure is high, it'll turn on the hobbs meter.
If you wanna be slick, you can add a relay to your current oil-pressure switch. When the oil pressure is low, it'll turn on the "low oil pressure light". When the oil pressure is high, it'll turn on the hobbs meter.
That was the goal. I wanted to track engine run time.
Last edited by My4Fordtrucks; Nov 17, 2025 at 06:04 AM.
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