Replacing tachometer

[Jack McDonald]

Hello.
It appears that my tach has stopped working. I've checked the connections at the back of the tach and they seem ok. So... I may be ordering a new tach soon. My question: When replacing the tach, what do you do about the engine hours on the old tach? Is there a way to set the engine hours on the new tach to the correct number? Or... do you stick a note to the back of the new tach that describes what was replaced and how many hours were on the original tach? Suggestions?

Also, where is a good place to buy a replacement tachometer?

Thank you...

[Aussie Mate]

Out of interest, has your tacho totally ceased working or does it move but to bizarre readings, like 3,000 when you are idling. If the latter you only need make an adjustment to correct. Either way I would try:

Remove the plate holding your instruments on the pedestal;
Turn it over and have a look at the back of the Tacho;
There is an adjustment screw there with some colored marker lining up the screw to the housing;
Turn the screw one way about 15 degrees and then line it up again on the housing;
See if it works now.

Alternatively, if you try to start the engine while still connected to shore power, it is easy to mess up the taco, so don't.
Good luck and let us know how it goes.

[Jack McDonald]

The symptoms were/are:
- prior to turning ignition on, tach would point to random places on the scale, not consistent
- with ignition on, engine NOT running, tach points to 0
- with ignition on, engine running, tach points to 0, regardless of engine speed

I've removed the instrument panel to have access to the wires and back side of tach.
I've turned the Alternator Range screw (settings ABCDE) several times clockwise and counter-clockwise in an attempt to clean the surfaces of the Range screw. The screw was then returned to its original setting (B). Tach still points to 0 with ign on, engine running.

During my first troubleshooting, I didn't have my multi-meter with me. So I checked the connections by merely pulling and wiggling the various wires and connections. I'll go back to the boat in a few days with a multi-meter and check the connections. I'll also check for voltages at the various connection studs on the back of the tach:
- GND to IGN (look for 12-16 VDC)
- GND to SEND (look for .3 VAC at idle, should increase with higher RPMs)

The procedure for troubleshooting the tach were found at the Teleflex website. Sorry, I don't have the link.

You caught my attention when you mentioned to not start the engine while connected to shore power. I've been starting the engine while connected to shore power for years, with no apparent problems. Perhaps fate has caught up with me and the casualty is the tach. Per your advice, I will no longer start the engine while connected to shore power.

[Jack McDonald]

Went to the boat today with my multimeter. (hint: I think I should keep one of these on the boat!) The multimeter proved to be a much better troubleshooting tool than just pulling/wiggling wires. Bad connection found on the SEND wire. Tach works fine now.

Except...
In my initial troubleshooting, I messed with the calibration screw. It now reads about 1400 during idle. I think I need to get a reference tachometer and recalibrate my tach.