Yamaha Tach Problems

[PCBeach]

Yamaha digtial tach connected to a 200 Saltwater. At idle the tach looks fine but when I am under power part (upper and left side) of the LCD gets dim. and I can't read the RPM. Also the trim indicator does not seem to be working. Any ideas? Would this be the tach or sending unit? Digital speed gauge next to the tach works fine.

[boats.net]

That sounds like a bad tach if half of LCD is dim

[PCBeach]

After going out this weekend I am thinking it is a connection now. Sprayed the powerhead with some OMC anti-coorode and when I started the engine the RPM did not show at all, but the arrow over the overtemp, oil warning (red) and low oil (yellow) were all lit. Checked engine oil tank in boat and engine, both fine. Ran all day with no problems. Any suggestions what to unplug on the power head to check connections? Any recommended cleaner? Thanks/