How to test a tacho/RPM Gauge?

[Superjetjim]

I have a 150 v6 Merc and the dash tacho isnt working, it has power (back light lights up) but doesnt read anything when the motor is running. I have a brand new harness and control box so its not that - how do I test what remains (Guage and Yellow wire up to stator) - Can I simulate the pulse of the grey wire somehow to check the guage?

Motor is a 81 V6 150

Cheers,

James

 

[Silvertip]

Re: How to test a tacho/RPM Gauge?

Does this boat have a Voltmeter"?? If so, what does it read at 2000 RPM. If less than 12.6 volts the rectifier/regulator may be bad and that's where the tach signal comes from.

 

[achris]

Re: How to test a tacho/RPM Gauge?

That engine only has a rectifier, so I would be checking that first...

 

[asm_]

Re: How to test a tacho/RPM Gauge?

With out a voltage regulator, your running voltage at 2000RPM will be much higher then 14.4v on a charged battery.

A replacement gauge is expensive, replacement rectifier is cheap, especially if you buy the Radio Shack's none marine version for testing purpose.

Here you go...

http://www.radioshack.com/product/index.jsp?productId=2062584