I believe one of the trim sending switches is for the limit and the other is for the guage. I guess you could play with the adjustment so that it is adjusted higher causing the pump to stop earlier.
But I am not sure 100%. it wont hurt anything by trying. If moving one makes the guage react then try the other.
if this works then put the drive all the way down and then adjust the guage sender till it is at the bottem of the indicator.....you will need the key on to see the guage work
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"Changes In Latitudes, Changes In Attitudes "

1996 238 Vista dlx "Casper's Toy Too"
2006 5.0GXI w/closed cooling, DP-sm 1.95 drive
Previous boat:
1998 Sundowner 205