5.0 L Merc Gauge Puzzle

[KetchiMan]

2004 Trophy 2359 w/Merc 5.0L

Dewinterizing my boat and my gauges aren't working. I sent the fuel/volt/speed gauge in a few weeks ago (when I noticed the fuel gauge wasn't reading) for repair. Got sent a new set, and the fuel gauge was reading in reverse, so I sent it back, but the guy tested it at the gauge shop and it worked fine, so he's sending it back.

Today I started the boat (without the fuel/volt/speed gauge in it) and my oil/temp/tach gauge didn't respond. Boat idled fine. Oil pressure and temp pegged to the right even with the key off (full hot, 80+ oil pressure) and my tach didn't read anything when the boat was idling. This oil/temp/tach gauge is only 2 years old.

So, what would cause both of the 3-function gauges to stop working?

Thanks!

 

[bruceb58]

You have a picture of these gauges? Brand?

What does the voltage gauge read when the ignition is on? Or should I say did since you don't have it back yet.

Are you sure you wired everything back correctly? Have a picture of the back of the oil/temp/tach gauge?

Probably should have posted this in the electrical section.

 

[KetchiMan]

Puzzle solved. Turns out you have to have both gauges wired in or the tach/temp/oil won't work.

Maybe the ground is run in series? The ground post has 2 wires on it...

 

[Bt Doctur]

All the gauges need a system ground.individual or daisey chained to the black ground buss