guages not working

[hes132]

my 78 mako has a johnson 1992 225hp engine the lower unit has been completly replaced the upper has been completly rebuilt. when i turn the key on to start the guages psi tach voltage are in the normal position when the engine starts the tach and voltage guages peg to full the psi guage continues to work properly when i say peg i mean the guage needle moves clockwise to max position just got the boat am trying to get some use out of it thanks john

 

[baxter66]

Re: guages not working

I would check charging voltage with a volt meter while at idle it sounds like you are over charging that could affect your tach and would explain your voltage meter pegging.I would also recommend getting a factory service manual it will explain all the test to trouble shoot this problem.

 

[Silvertip]

Re: guages not working

You've very likely lost the ground connection to all the instruments. The Water Pressure and speedometer gauges are not electric so its not affected. Without a ground, every electric instrument becomes a potential path for another circuit hence the weird readings. Every gauge has a ground connection that is daisy-chained to each other and then tied to the black engine ground. Check that first. OEM engine manuals will not cover gauges as they have no idea which manufacturer produced them.