Sounds like a short in the trim pump, or pump relay. Less likely, could be a corroded ground in the trim pump finding an "alternate" path to ground through the accessories. My sail boat did that with the lights.
First thing I would do is find your main ground (at the batt and engine block). Disassemble the connections, clean and reassemble. Do the same with the trim pump wiring and try it from there.
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Walt B
"Debt-Charged"Black '07 H210SS6.2L Bravo One turning a 21P HIFive
Wakeboard Tower with Perfect Pass Stargazer version
Missouri River; Kansas City, Mo.