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Old 17 September 2012, 05:33   #1
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,538
Yam Tacho - Merc Engine.

OK, here's the thing. I have successfully used an old Suzi Tacho on a Suz, A Yam and my current Merc Clamshell.

In a fit of trying to make the boat look a little less "Mad Max meets Waterworld" I got a Yam tacho with a Blue dial to match the rest of the instruments. It's one of the "two wire ones - Here's the weirdness:

- When I connected it direct to the alternator output / Earthed to the block at the engine with the old Merc Rectifier, it read OK.
- When I put it in the panel & connected it as above - Nothing. (I tested immediately with the old suz tacho, and the wire is sound)
- I have since fitted a Honda rectifier / regulator to stop battery toasting, and the same thing happens.
- During my last cruise, it randomly for about 2 seconds jumped up to what I assume revs were (4.5K @20-ish knots) & died again.

(and I have put the old Suz tach in an ice cream tub & had it working OK since)

So, do I need a capacator / coil/ big resistor in the line? I assume the tacho takes it's power direct from the alternator (signal) line rather than a dedicated +12, and I am wondering if the internal resistances in the tach are not matched to the engine's alternator. The fact it works OK at the engine would hint to me that there is a resistance / capacitance issue with the run to the console.

I keep reading about certain tachos needing resistors / capacitors across the signal - Gnd terminals with certain engines. Anyone know if the same applies to the Yam tacho connected to anything other than a Yam engine?
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