8.1 Gi Trim Sender - Not working most of the time

[JTinMO]

Hi All - You have been very helpful in the past, so will go to you all first.

2010 232 with the 8.1 Gi. For the past year the trim position has sometimes worked, sometimes not on the dash. It never works out of the water, and when it does work, it seems to be only when on a ramp when putting the boat in or out for the day. On the water it seems to never work. Do you think this is a faulty trim sender, or a gauge issue? Pic attached of the sender in case it helps. It bothers me that it works sometimes. I wish it was either working 100%, or nothing at all.

Also, on the left side of the motor, there is a hole in the same position with nothing in it. Should there be a cap on there, or should it be left open like it is in the pic?