What does the trim limit kit do?

[appel1978]

So I am newish to boating. I installed a trim sender assembly on my 1990 omc cobra a few years back. But it only reads on the gauge for the last 20% of travel down. As soon as it get past about 20% up the gauge stops working because there is a huge gap between the switch arm and the stern drive that is being raised. Is this normal? I figured it should show a smooth consistent read on the gauge till it reached the top so I know exactly where the position is at all times.
I saw this part for sale called a omc trim limit kit #987142. What is that for? Where does it go I can't see any pics or diagrams anywhere online on where it is to go.

 

[Melven]

Don't know what the limit switch is for, but I think my sender assembly is shot as the trim gage does not work. At times it will flicker as if it works, but nothing. How difficult was it to change the sender assembly? I have a 1990 OMC 3.0 cobra.