Does anyone have a part number and/or source for the RPM sending unit? My gauge hasn't worked since I bought the boat and after testing the wiring and unit itself I'm quite certain it's the problem

Patrick,

If it is a 2GM, here are the Yanmar part numbers:
Tachometer part number: 128170-91100
Sender part number: 128170-91160

The tachometer uses a magnetic pickup sensor on the flywheel - mounted on the port aft side near the top of the bell housing. The connector at the sending unit should be checked for loose terminals.
Here are the checks according to the shop manual:

1. Check the connections on the back of the meter.
2. Check the voltage on the wires on the back of the gauge - black is ground, red/black is 12v. If there is not 12 v there, investigate.
3. Check if sender is fitted loosely.
4. Measure the internal resistance of the sender - should be 1.6 +/-0.1 KOhms.
5. Measure the output voltage of the sender - to be 1v or higher.

I'm guessing 90% is a problem with the meter ... they were never great waterproofed ... nor was that start panel which requires a key switch change every 20 years.

Often we see mist inside the face. but if we had a great way to replace with a nice cheap compatible meter ... i'm interested. I'm thinking the meter is a once every 30 year maintenance item. we see a lot of meters on consignment ... just getting the one that works with the 2gm is the question.

on 505 it will start running at zero and after warming up a bit ... say a half hour or so of running ... it will come close to registering 2000 but not really up to the action a new meter gives.

would love to see if this one works [link to current ebay listing]



[zoom in on the back of the meter to see the adjustable teeth settings. I screwed one of these meters up by not pushing the adjustment in to change it ... had to epoxy the setting to lock it. but that was on another motor ]

Thanks for the quick feed back.