The Hardy Motor Boat Owners Club Message Board.
Message board > Engines > Tach / Rev counter not working
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Message 1 of 6
Posted by member Sandpiper on Tuesday 3 November 2015
I have checked the ‘W’ output at the alternator and get an ac voltage range from about 7.28 volts to 7.6v as the revs increase – not as much change as I would have expected. At the rear of the rev/tacho gauge there are an awful lot of wires, a plug block of six and 3 wires on a spade connector at the top of the gauge. As yet I haven’t investigated which one, if any, could be the alternator tacho input. Before I delve into pulling things apart:-
1. Does anybody have or know how I can obtain a wiring diagram?
2. Does anybody have any idea what/why there are all these wires on the back of the rev indicator?
3. Any ideas what might be wrong or even what the voltage readings might be realistically?
Thanks - Dave
Message 2 of 6
Posted by member John on Tuesday 3 November 2015
The tachometer usually measures the alternator a.c. frequency hence rotational speed and I would not expect the voltage to change very much.
Possible reasons - a dirty connector, try unplugging and re plugging those wires, that usually cures mine. One wire will be ground, positive supply, tachograph input, maybe instrument light. Others may not be anything to do with the tachograph.
This wiring diagram link may help (copy & paste)
Message 3 of 6
Posted by member Peter on Tuesday 3 November 2015
Not sure if this will help but seems to be a wiring diagram for a TAMD22. You are measuring an AC voltage with your meter which is actually measuring the average voltage so as the frequency increases (with higher RPM) so the average voltage will rise slightly. (the wave form gets closer together as frequency rises so the average voltage will rise a bit). Your meter may have the facility to measure frequency and that's what you need to see changing but by the sounds of it that is happening.
Message 4 of 6
Posted by member Dave on Sunday 22 November 2015
The tacho is the original 1997 fitting and was made by VDO but the only replacement is a very very expensive Volvo tacho at £180 plus. I am currently searching for a more reasonably priced replacement for 85mm hole and revs from 4600 to 6000 - I don't think I will be lucky!
Correction to my original input - the plug has 4 pins, two for power input and the signal and return. The 3 wires at the top of the instrument were for the lamp.
Message 5 of 6
Posted by member John on Sunday 22 November 2015
Message 6 of 6
Posted by member Anthony Purnell on Monday 16 October 2017