This just started acting up last week, the trim works fine but the gauge jumps around quite a bit. Do I have to replace both senders or can I try replacing one at a time? I read somewhere that the drive needs to be removed to run the wire, is this true?
Thanks

I am assuming you have a Merc.
On the Bravo, the trim sender is on the starbord side (limit switch is on Port side)

Before replacing, try dismantling, cleaning and lubing.

thanks rickr, what's the adjustment for on the sender?

Trim drive all the way down. Rotate sender so that it reads down and fits into the boss with half adjustment in each direction. Run trim up until the trim limit switch engages. Should be 21 and 1/4 inch from center of trim ram bolt fore and aft. Play with the trim sender to have it your gauge at between 3/8 and 1/2 or whatever you want. Just look at and play with it, it will become evident. Don’t forget to use anti-seize on the screws holding the trim limit switch.

Ok, that’s how to adjust, now address why it is jumping around. Check to be sure that the pivot bolts that hold the gimbal on are not loose. That can cause the gauge to give a wrong indication as the sender assume that the housing is stationary as well as the bolt that it engages into. Pop it off and look at it; you will see what I mean. Look for frayed and bare wires from the sender. Sometimes you can band-aid it with liquid electrical tape to finish off the season.

I am sure someone can explain it better but it's hard to describe until you take it apart and look at it. You may need an impact srew driver to get those screws out. If they don't come out with a good twist get one before you bust the head off.
Tim T.

Ok I just pulled the sender, I didn't touch the limit switch because it's working fine (I think it's fine at least). The sender came apart with no problems, no frayed wires either just a little damp and full of grease. I was sure to make note of how it was aligned on the drive but the white disk popped out and I don't know how it was set up. I put it together without the cover and the guage was worse, the direction is backwards and it goes from full up to full down, it's no linear at all. What did I do wrong?

I believe you have turned the hex shaped piece (that fits in the pivot bolt) too far before reinstalling the sender. Have someone watch the gauge while you turn the hex part to get in in the proper relationship to the housing.