Electrical issues are a PITA because you have to get in there and troubleshoot. Having your switch not light up indicates your problem is with power and not the blowers themselves. I am not familiar with your boat but a test light and a wiring diagram would go a long way for you if you are somewhat mechanically inclined. You are gonna need to go through the entire circuit. Could just be a dirty connection or a bad ground. Could start at your switch and go from there before having to get into the tight space.
Good Luck. Let us know how it turns out.
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Walter

2003 248 Vista - VP 5.0 GXi
2009 Toyota Tundra SR5 5.7L 4x4