Tach This!!!! question

[Mr. Fancy Pants]

I pulled the multimeter out and tested the three posts on the back of my US Marine tachometer. The black (ground) has good ground. The Purple (positive) shows 11.99v. The Gray (signal) wire shows 11.56v. These readings are obviously with the key in the on position.

Are these readings normal? Should the signal show voltage without the motor running? Also, what else can I do to trouble shoot the tach not working at all. I'm assuming it's the tach itself but I'd like to check any other possible isssues. I did check the main wire harness for corrosion.

Any input if def. appreciated.

The motor is a 3.0L Merc In/Out.

 

[bruceb58]

Re: Tach This!!!! question

You are just measuring the negative side of the coil so when the engine is not running and the points are open(if so equipped) you will just read the voltage of the coil. When the engine is running, there will be pulses sent to the tach and you won't be able to measure those with a meter.