Help me understand auto electric please!!!

[litevette]

As I do different projects on my car, I keep noticing the major need to rewire some things. Add to that how I read on here about you folks modernizing your electrical systems and you can understand why I want to tackle this. I would greatly appreciate any and all help in understanding the following questions, and hope that you take into consideration that I know NOTHING about wiring, electricity, wire guages, amperage, etc. Please speak as if you are trying to explain to a child! Oh, and by the way, if you don't have all of the answers that's o.k. Help on tthe things you can please!

1. If I rewire something, and want to use relays (I've read on here that they are good to use to avoid "voltage drops" to the item being powered), where would the fuse go? Before the relay? After?

2. In the above relay situation, what powers the relay? If for instance I wanted to add relays to my lighting system, would the power from the headlight switch now just power the relay? Would I need to fuse between the headlight switch and the relay also?

(for questions 1 & 2, I've pasted below diagrams I made. Which is correct if either one is? A or B?)

3. What size or guage of wire needs to go to the various components? Should I just look at the old wire size feeding the component and match it in size? Are there certain wire sizes that are universal for say guages, headlights, horn, fan, etc?

4. If I use terminal blocks to feed various components, and there are two compnents running off the terminal block, would the wire feeding power to the block have to be double in size of the wires feeding the two components? For example: The two components need 10 guage wire each, would the wire feeding the terminal need to be 5 guage? ( I was told that the higher the number the smaller the wire, so I'm geussing that a 5 guage is double the size of a 10 guage?) SEE FIGURE C

5. Can a switch, a relay and the component all share the same ground source? Any reason why not? SEE FIGURE D

6. Anywhere you don't want or need to use a relay? Could I use one everywhere? (not that I would).

7. What size fuse for what component? How do you determine this?