If your doing relays you don't need anything from factory wiring. Unless you don't care about ever using them with the key off and you want it all going off with the key then you would I guess.
Some things like wireless winch remote power lead needs to go off with the key though we know. But radio, lights and many accessories you want to add you may want to be able to fire up without the ignition being turned on.
You need to power the relays with their own direct line to battery. There is your switch power or relay coil power just fuse it down.
What I like to do is to feed the relay coil hot on one side on a small fuse(fed from relays main power lead)and then use the switches to bring the negative to the relays to negative side of the coils that energize them. That way if anything ever goes to ground nothing happens except something stays on and lets you know what is shorted but doesn't blow any fuses.
If you have a relay you don't need a control wire from the harness. You can take the power for the switch(s) right off your power for the relay and come back from the switch with your "control" wire or one that actually energizes the relays coil.
Or with switches feeding the hot sides of relay coils and the other stays grounded to negative.
Why add anything to the system if adding new power from battery to relay for the accessories. You tap that and put a small 5 amp fuse to power the switch and come back out of switch and feed coil of relay. I mean unless you want them to all go off with the key which is not so good having to have the ignition on to run anything.
Might have repeated myself. Good at that.
Something like this. Master switch is optional but good idea. You leave it off like the ignition when your not using it but at least you can run things if you want with out the ignition having to be on. Just good to know everything is off with the master so you don't have any risk of draining your battery. This is the switch system wiring for them only having negative grounded current on them. Never a risk of shorting out anything.
If you want your switches lighted check and see because you may have to use them as the positives feeds to relays so there is power for integral lights if they have separate neg and pos for lighting no problem. Just feed them positive off light switch relay or if you don't mind them lit always then the ignition.
Just a rough sketch and of course so many variations possible. Most will want to feed the mains to each relay from a separate fuse. I didn't draw that in but usually what you would do.