Re: Trim gauge or sender?
Here is an Idea for you to try. I am not familiar with the location of the sending unit on you Yamaha. I beleive that it's possible that it is located on the motor mount bracket somewhere. If so, raise the motor to the full up position, use a multi-meter on the sening unit to test for resistance changes from one end of the sender to the other. Hook the red lead to one wire on the sender with the black lead to the wire on the other side of the sender. The sender should read increasing resistance as you depress the sender or trim the motor to the down position(if power WERE present this would be cutting off voltage flow to the guage causing the needle to drop). As you release the the plunger on the sender it should spring load back to the up position, decreasing resistance( once again, if power WERE present, therefore sending voltage to the trim guage driving the needle back to the up position). I beleive that it works just like a reostat or a light that you can dim in your home by the turn of a knob. If the resistance check works the way it should, then check for the same result at the power in wire on the back of the guage for resistance between the input side of the sending unit to the power lead on the guage. If you get the same result with both increasing and decreasing resistance at this end of the wiring harness, that should mean that voltage should pass succesfully from the fuse box to guage with the motor raised all of the way up and the key in the on position. In that case, the guage is possibly shot or you have a bad ground on your instrument cluster ground circuit. By checking for resistance you decrease the possibility of shocking yourself. The same result can be determined by checking for DC voltage in the same manner. It's worth a shot.
