Gauges not reading right

[atistang]

I just bought an 89 Cheetah 18' fiberglass boat with a 3.0 merc

When you start it the volt gauge reads about 10ish, the tach says it is idling at 2500rpm and when I'm WOT it says 6000rpm. the fuel gauge is all over the place, even if sitting still it will bounce between 1/2 and 3/4. now all of the gauges really go crazy when you do something that takes some juice such as trim, turn the blower on, run the bilge pump, etc... the tach will drop about 2k rpm, the oil pressure gauge will drop about 20psi, the fuel gauge will drop 1/4 tank, etc....

anyone have any ideas? bad ground?

this is my first boat and i am not familiar with boat wiring, just cars.

 

[Lyle29464]

Re: Gauges not reading right

Sure sounds like the ground. I think I would just run a temporary wire from the battery to any one of the grounds on the guages and see if that fixes it. If so clean and check all of your grounds under the dash and check the ground source for the guages. If the ground wire does not fix it make it a hot wire and run to the I terminal on a guage or the buss bar.

 

[atistang]

Re: Gauges not reading right

Sure sounds like the ground. I think I would just run a temporary wire from the battery to any one of the grounds on the guages and see if that fixes it. If so clean and check all of your grounds under the dash and check the ground source for the guages. If the ground wire does not fix it make it a hot wire and run to the I terminal on a guage or the buss bar.

ok, i'm guessing i should also get a solid 12 volts or better at the gauges also?

 

[Silvertip]

Re: Gauges not reading right

The electrical system on a boat is a 12 volt system. Normal voltage in that system is 12.6 volts (static) depending on state of charge. Engine running 13 - 14.5 volts or so depending on engine RPM. Yes - the gauges need +12 volts and good ground to operate properly..