when I turn the key to the on position. Is this caused by a ground out ? what would be the most obvious cause, sending unit, bad wiring, short in the dash ?? it has read properly at one time, starboard side is fine

Check the sending unit wire connection. Depending upon make of gauge/sending unit, could be the ground side also. Problem is most likely wiring.

Yep just like what SFOcean said......first thing i would do is find the sending unit and disconnect the pink wire.....if the gauge goes empty then inspect the sending unit....if still full then go to the back of the gauge and disconnect pink wire......if still no change then its a bad gauge....it if does go back to empty when you remove the wire from the gauge then you have a short to ground somewhere along that wire going from the gauge to the sending unit.

Pegged Full is usually caused by the sender not being grounded

Hmmm...well i only speak from the last one i fixed on my dads deck boat...dont remember what brand it was but it worked as i described....if they are opposite then I'd start at the sender and send a good known ground down the pink wire and see how the gauge reacts, if it moves to empty then the sending unit or the ground wire is at fault....if no movement then go to gauge...remove pink wire and put a good ground to the terminal...if it moves then its the wire to the sender...if nothing its the gauge...

Wally you are absolutely correct! I agree 110% I have done this a bazillion times. Excellent explanation. Clear, concise and without any uncertainty.

So here's what I have, green seems to be power, white goes to the dash ( gauge ) and blk is ground, so I removed the white wire from its terminal and with the key on and I ground the white wire it pegs the gauge to full, does this tell me I have a bad sending unit ??

Try alligator clipping the white wire from the problem side, to the other sender. See what the gauge shows.

Im betting on a bad sending unit.

Yup good call MT I moved the white wire the other sender and it reads as it should, so both gauges and wiring are fine, now any one have a place to get one ?

I replaced the ones in my Fountain, with some "sunpro" brand senders. Put them in in 2010, and still working great. Guages are pretty dam accurate too. They were like 20 bucks a piece.

Ill try and find the part # later . They are basic sending units, nothing trick about them