Damn, that's a tough question. Really, the only proper answer is how many do you want? There are certain things you need, such as lights, radio and bilge pump, but after that the sky's the limit. If you plan on having trim tabs then you'll need to install the (2) rocker switches that come with them. Then there's the lights.. Running lights are necessary, as is an anchor light. But you can install led lights for nighttime ambiance, and lights in the cuddy cabin. Then there's your radio. One for the VHF, one for an AM/FM. How about a chartplotter? Radar?, One or two depth finders/fishfinders, CB radio, bilge pump (manual and automatic), underwater lights, coffeepot (Yes, coffeepot) electric cooler for the beer, etc. See what I mean? The only person that can really answer your question is you.
If it were me I'd sit down and make a list of the things that I have to have and the things that I want on my boat. Once you know what you are installing, then size your fuse block and your wiring accordingly. (My advice would be to allow at least 5 blank slots in the block for future expansion).
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1987 V20 w/1987 150HP Yamaha on a Shoreland'r Trailer
1978 16.5 Airslot w/1996 120HP Force on a Four Winns trailer
1996 V21 w/1993 200HP Mercury on a Shoreline Trailer
All towed by a 5.7L Hemi Durango.
If God didn't have a purpose for us we wouldn't be here, so
Live simply, Love generously, Care deeply, Speak kindly.
(Leave the rest to God)
Silence, in the face of evil, is itself evil. Not to speak is to speak, not to act is to act. God will not hold us guiltless.