Instrument panel clicking, dropping voltage momentarily

[HalfCaff]

So the other day I was wiring up my new trim tabs, and looking for a place to pull a connection to the ignition switch for the auto retract. So I turned the key on to aux power and started to work with the multimeter - when I noticed a distinct "click" sound, accompanied by approximately a .5-1V drop on the multimeter. It it is a mechanical click - sounds almost like a relay, but there aren't any relays in my panel. It kept happening every 30 seconds or so - click and voltage drop for a few seconds, then another click and back to full power. This was before I hooked up the tabs - so I hadn't altered anything yet.

I poked around and put my ears up behind the panel and I am pretty sure it is coming from the tach, or the hour meter that is built into it. It is an old Honda needle tach with the analog dials hour meter. My instrument panel is very basic - tach, speedometer (that is not hooked up), gas gauge, and voltage meter. That's it, all analog. Motor is a Honda 75hp 4 stroke, probably 1998 by the serial number.

Any ideas what this might be? I suspect the hour meter, but not sure why the voltage drop. Also not sure if it is a problem or not - I rarely am sitting with the key in the aux position. I usually just get in and fire up the motor. If I am trolling I am on the kicker and key is off. I might turn it on for a couple seconds once in a while to read the fuel gauge but that's it. Its possible this click has always been there and I just never noticed before.

[martin3]

It is very likely the hour meter,  the analog ones do have a noticeable click.

[HalfCaff]

But why would the hour meter be clicking if the motor isn't running, and every 30 seconds or so?  I could definitely expect a click when it actually rolls over from 1 hour to the next - but this is just when I have the key in the aux position, and repeating at a regular interval.

[martin3]

Leave the key in Aux position and watch the hour meter.
The regular interval comment makes it sound like the Hour meter.

The hour meter doesn't care if the motor is running or not,   it operates when power is applied.

[HalfCaff]

Yeah, I guess I just probably don't understand how the hour meter is supposed to work and if the clicking is "normal".  From the reading I have been doing it seems like it might be - but the accompanying voltage drop is what concerns me more.  It will last for about 10-15 seconds at the lower voltage level, and then return to the higher level at the next click.  I guess maybe the hour meter is drawing power to do whatever it is it is trying to do?

I think I will disconnect it and see if the problem goes away, that will at least confirm the source.  Then I will need to decide if it is something worth doing anything about.  Like I said, I rarely if ever am sitting with the key in the aux position under normal circumstances.  I have a house battery for pretty much everything except the main motor and guages.

[fishmeister]

Leave the key in Aux position and watch the hour meter.
The regular interval comment makes it sound like the Hour meter.

The hour meter doesn't care if the motor is running or not,  it operates when power is applied.

The old mechanical hour meters are actually driven by a tiny motor with mechanical gears to drive the display numbers.  There are ratcheting levers to prevent backwards travel of the display.  I believe Martin is correct in that the display motor operates as soon as it receives power (regardless of whether or not the motor is actually running).

[davidsea]

  I have a cheapy mechanical hour meter up behind the dash, purely for watching maintenance intervals, and it does exactly the same thing.   It's probably just a tiny solenoid that 'kicks' the mechanism forward at regular intervals.   With modern EFI motors, the ignition 'ON' current draw is pretty substantial anyway, but that seems like a bigger voltage drop than I'd expect for just the gauge, but since it's only with the key on, really nothing to be concerned about. 

[HalfCaff]

Had the boat out last weekend, and cam now confirm the clicking is there when the motor is running as well.  I probably just never noticed since it's a lot harder to hear it over the motor.  No other issues, everything ran as it should so for now I'm going to file this in the "not a problem " category.  Thanks all.