Are all my gauges bad?

Good afternoon all. I have 3 in 1 tachometer, fuel gauge, and voltmeter on my 2001 17' Trophy w/ a 90 hp Mercury O/B. I tested the tachometer part of the gauge and it is receiving the necessary 12 volts. I am also assuming that the ground is fine because the back-light functions fine on the gauge.

My question is: If one of the components in the gauge goes, should the other 2 gauges not function as well?

Re: Are all my gauges bad?

Tested the tachometer part of the gauge???? How did you do that because the gauge has only one +12 volt terminal that is active only when the key is in the RUN position. That +12 volt (normally labeled "I" for ignition) serves as the power feed for all of the gauges within the unit. The tach has a send terminal and if that's what you measured, that would not be the +12 volt input. Since all gauges are dead, you need to check the "I" terminal. Ground is ground for all units and since the backlight works, that would indicate ground is ok. It would be really rare to have all three gauges defective. I really think you are missing 12 volts. The voltmeter for example requires only +12 volts and ground to operate. The fact that it doesn't says 12 volts is missing.

Re: Are all my gauges bad?

Thanks for the help Silvertip, but it turns out all three of the gauges were bad. I hooked up a new tachometer and it worked immediately. Tomorrow I will hook up the other two gauges, but it will be a little more complicated as I have to cut out two new spaces for them.

Re: Are all my gauges bad?

I guess it's a moot point at this time since you have new gauges, but how did you prove they were bad.