ok not sure if i am a dumbass or what, had the boat running and on the water (parker gathering and before), everything was ok, minor isssues (but was running good), took the boat apart and redid the floor and regasketed the motor, was running it tonight to set total timing (driveline is out ) looked at the tach and it said like 2500, the motor was idling (maybe 900rpms) nothing has changed with the boat or wiring, what the hell happened, i am running a msd 6al box with 6k pill, msd dist, msd rotor, msd cap, msd wires, a/c plugs, tach signal is coming from the signal connection on the box (same as always), i replaced the connector at the box just to be sure it was good/clean and tight, no change, what am i missing or could have happened, i looked at the gauge itself (maybe i did something when donig the floor) all looked normal  i am  about to join the I HATE BOATS CLUB and don't really want to 

Bad ground.....Check the ground wire going to the dash. Possibly at the engine.

maybe got set for 4 cyl

Mine reads high every now and then so I just hit it and it goes back to normal!

everything worked fine before taking it apart and there where no mechanical changes made, lifted motor out of boat, put wiring to the side so i could do floor, reinstalled same as it came out, i am going to play with it more tonight so i will post up what i find.

make sure your wire is on the negative side of the distributor. 

I am running the msd 6al box, it has a designated plug for the tach lead on the side of the box, nothing for tach to dist.