Replacement Hour Meters - Wiring?

[markpj23]

No surprise for the Volvo owners out there I'm sure.... but both of my LCD hour meters integrated into the tachometers on the Volvo control panels have now quit.

I bought a couple of cheapie counters that I intend to mount in the engine rooms. My question is what lead to use as the ignition-on source? I have externally regulated (Balmar) alternators, and as now installed, the tachometers drop to zero once the battery bank is charged and the regulator kicks off the alternator.

Any ideas / suggestions?

[Sailmonkey]

find any ignition on "hot" wire and attach the positive lead of the meter. The meters draw virtually no current so really anything that's switched with the ignition will do.

[GordMay]

You can wire a “Hobbs” hour meter to an engine “on” or “run” terminal on your ignition switch, as Sailmonkey explains.

This is the most common method. Note that the meter will run anytime the switch is in the "on" position, even if the engine is not running. Under most circumstances, this shouldn't pose a significant problem.

The preferred method is to wire 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.

[markpj23]

Originally Posted by GordMay

.... The preferred method is to wire the hour meter through a normally-open engine oil pressure switch....

That's the ticket! Should be the easiest lead to find as well.

Many thanks for the replies.

[Chief Engineer]

You do mean an Oil Pressure SWITCH not an oil pressure SENDING unit....I am just reinforcing the distinction.

I have seen way too many switches wired through the ignition....the meter ends up being useless......with a bazillion hours on it....because the ignition switch was left on.

The most anal use I have seen is Hobbs style meters (4) on an aluminum hull for the bilge pumps.......

[theonecalledtom]

HA.

On OneLove there is a switch on the main 12v panel called "Instruments". As far as I can tell all this does is run the hour meter.

Consequently I have no clue how many hours the engine has on it.

I was considering wiring to the ignition instead - the oil pressure wanring buzzer means this is generally off when the engine isn't running, or am I missing something?

[Ex-Calif]

Technically on a diesel engine there is no "ignition" circuit. There is usually a panel circuit that powers the panel, buzzers, instruments, glow plugs and starter.

Gord's distinction is important.

1 - Wired to the panel - will count hours any time the panel is powered
2 - Wired to a normally open oil pressure switch - Will count hours when there is oil pressure. Note the normal low oil pressure switch works opposite of this - i.e. it is open when there is oil pressure. You likely will have to add this switch if it doesn't exist.

There are switches wired to the alternator output - parallel to the RPM gauge. Because this is a variable output the counting is variable. The meter is usually calibrated at a specific RPM - like cruising RPM.

I personally like option 2.