Junction box for what? Do you mean a sub panel?
You do not use a ground wire in the connection from the meter base to the distribution panel. A bonding wire may be required if the service is using PVC conduit.
Connect the ground wire from the light fixture to the ground wire in the ceiling box.
Yes, but the splice must be made in an electrical junction box.
Yes, the wire gauge numbers are smaller. A typical automotive battery cable would be 4 gauge, the wires after the fuse box would be 10, 12, 14, 16, 18 and 20 gauge depending on the accessory.
A 240 volt wire is the insulation factor of the wire. If you mean a 240 supply source from a distribution panel to a junction box then the answer is yes. You have to keep in mind that the box has to be accessible, meaning that you can get to the box to check the splice within the box. Don't bury the junction box behind the wall board.
Connect the ground wire to the metal box.
The fuse for the petro gauge can be found in the fuse box. The fuse will be labeled as the instrument panel fuse.
Yes, but the breaker that protects the wire size has to be sized to the smaller of the two wires. Also the splice has to be made in a junction box that can be fitted with a cover.
The size wire you would use for a sub panel box would depend on the square footage of the area it will be servicing. <<>> Wire is sized by the amperage of the load, not the square footage of the area it will be servicing. . Depending on what the amperage size of the sub panel that is to be installed, will govern what the conductor size that is to be used.