The CMC Hydraulic Jack plate gauge is not working on my boat.  The jack plate does go up and down with no problem.  The gauge appears to be OK, but the pointer goes all the way to the top as soon as I turn on the ignition and stays there.  Tried calling the factory and they are not answering the phone.  I am assuming they are down with the ice storm.  Anyone have any ideas as to what might be causing the problem?  Worked fine when I put the boat up in November.

CNC itself I can't help you with but in general I might.  The sending unit on the jack plate is probably nothing but a variable resistor.  The meter's signal terminal is going to have 12 volts on it going through the sending unit to ground.  As the unit goes up and down the resistance to ground through the sending unit changes so at one end of the extreme the meter will be all the way up, at the other, it will be all the way down.  

A quick check to see if it's reading a short or open, take the wire off and if the meter is still all the way up, just touch a ground wire to the Signal terminal on the meter, if doesn't kick all the way the other direction there is a problem at the meter.  Make sure you have 12V on the Power sourse terminal the  make sure you have a good ground on the ground terminal.   If it does kick the oposite direction, then you have an problem with the wiring or sending unit at the jack plate.

Also, if when you take the signal wire off the back of the meter it drops to the bottom but jumps back up when you put it back on, you either have a bad ground at the meter, a shorted wire to the sending unit or sending unit is stuck/bad.

To trouble shoot the problem you can take the signal lead off the back of the meter and use an ohm meter connected to the  wire you took off and a good ground, measure the resistance.  I would guess the sending unit to be a 5K or 10K pot so it should read somewhere between just a few ohms and 10,000.  Raise and lower the motor and see if the reading changes as you do.    It the meters reads reads and open or extremely high resistance, you may have a broken wire going to the sending unit or from the sending unit to ground.  If it's reading extremely low resistance and does not go up when you change the motor height, the wire going to the sending unit or the sending unit is shorted.

Kinda long but really not that hard to trouble shoot if you know how to use a multimeter.