Norm,
I believe you need two toggle-type switches to replace the joystick-style that came with Marinettes. Normally they mount side-by-side, with the toggles moving vertically.
The port toggle switch runs the port trim tab, and the starboard toggle runs the starboard trim tab, raising the tab when the toggle is raised and lowering the tab when the toggle is depressed.
This way, pushing both switches down lowers the bow, but pushing the starboard switch down raises the starboard side. This is what I am used to, and it works for me - many commercial boats are wired this way.
I have a breaker for the trim tab pump on my accessory (eyebrow) panel, and it wires directly to the pump back at the transom. There is a 6-wire (I think) cable that runs to the switches from the pump.
I have not documented the wiring because the Bennett manual is very good, but would be happy to add it if anyone would like to see it....
1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida