When I first start the engine the trim gauge jumps into life after a surge of electricity but then fail to work anymore.
Would this mean that the sender on the engine is not working as the gauge has power? Any tips to identify ? It's a 2001 Fitch 115
Do you mean it jumps from its "off position" to an "on position" and stays there no matter how much you move the engine OR it jumps to on and then goes back to off?
If it is the former then it could just be that the "sensor" is stuck/bent. Find it, wd40/grease and then move it manually in and out and see if the needle moves. Beyond that you probably need to stick a multimeter on it to see what voltage it is sending. As far as I know they are all just variable resistors moved by a lever and so put out a range of voltages depending upon the position.