you want a fuse for each device and heres why. Say you have the fog lights, rear lights and air compressor on and it draws 10 amps total (for easy figuring) so you would want a higher fuse then that, say 15 amp. So now with all three items on you wont blow a fuse.

ok but heres the problem with that. You turn on the air compressor and the motor is stuck, maybe the windings in the compressor can only handle 5 amps. Well you have a 10 amp fuse in line, so the weakest link is going to be the motor windings burning up.

So basically you can use the same wire (you should take the sub straight to the battery) but you should have each device fused with the correct size fuse.

You can put the fuse anywhere before the actual load, before or after the switch on the hot side. The best place is always as close to the power supply as possible though. I like that in case a wire breaks and shorts to the frame, then the fuse will blow before burning up the wire or whatever.

As far as a relay. I only use them when I want something else to do the switching IE. brake lights bringing on aux lights. To turn on fog lights I would just use a fuse, wire, switch and fog lights.

 

I guess the nice thing about putting a realy for the lights is I don't have a ton of flow coming into the cab where the switch is. Does that make sense?

Maybe I can put a different fuse on each switch but still feed from one wire.

 

The main reason I use relays is so I dont have current going through the firewall.

But, for the switches (and thus relays), it is ok to use a single fuse to feed them. Its the +12V prong on the relay that you want a seperate fuse for each circuit and relay.

 

Is this way ok?

 

no need to put fuses in between your switches and your fuse block. overkill

 

Bob- read Cynic X's post above...he explained why you would want a setup like Jovis posted.

Jovis- That is what I was thinking of.