Tach testing problems

[Goosegt]

Hello, this is my first post though I've been to this site dozens of times in the last year. I bought my boat last year, 2002 crownline 180 with a 4.3 mercruiser. The tach and trim gauge didn't work, tried dinking around with it last year to no avail.

Well I'm at it again and having a problem testing the tach. The faria page says to check for 12v with test light, then jumper the signal and ground. The signal and ground jumper should peg the gauge when the key is turned on. When I do that my volt meter shows like 10 volts and the jumper wire nearly melts.

I am testing it with the engine off. I read 12v at signal post.

The tach needle doesn't move when the ignition turned on, the hour meter does work along with the light......but there is zero movement in the needle.

Do I need to disconnect the +12v to do the jumper test?

Any help is appreciated, thanks.

 

[Silvertip]

Wow back! You are testing two different gauges. The jumper test for the tach is valid. It is not a valid test for the voltmeter. There is no "s" (sender) terminal on a voltmeter. That gauge has +12 volts and ground and ligjht as the only terminals. If you jumper +12 v to ground you create a direct short which is why the wires melt. If a voltmeter doesn't work +12 volts or ground is missing. If the tach doesn't work, +12 volts, ground and/or the "S" sender signal is missing. Very different scenarios.