Wire size is vital based on current flow and wire length. You should be running at least a 12 gauge wire to flow that much current to the roof. The standard to use in fusing is double the full current draw of the accessories in question. A 25 amp circuit would have a 40 - 50 amp fuse recommendation according to GM standards. To flow that much current, you must have a relay as previously stated. I recommend a visit to a local NAPA store where you can get a Megafuse that uses bolts that will hold any size wire you need and flows current up to 150 amps. J.C. Whitney carries a 70 amp relay that is ample for what you need. That is what is running on Project X powering my compressor and 4 100 watt lights. This setup has been used on Project X for two years now without failure.