Kyle:
#1.) Decide if you want to have a "switchbox" or similiar item, nearby the driver's position and whether or not you'd be able to hide it "discretely" and its associated wiring...
#2.) "Remote" all wiring, from each "head unit" (and the speakers) to the panel and terminate each wire on its own position on its own "component" barrier strip. REMEMBER TO LABEL EACH AND EVERY WIRE AS TO WHERE IT CAME FROM, WHAT ITS PURPOSE IS AND WHETHER YOU WILL NEED IT IN THE PROJECT...
#3.) Using mini-relays (rated appropriately for the circuit under control...) wire each respective circuit wire to the
correct contact of the appropriate relay(s), remembering that the "wiper" contact needs to return to the "final" O/P of the circuit being driven/controlled by whichever device you want to have on-line at the time.
NOTE: Before you even start with STEP #1, you should, seriously, sit down and diagram (schematics) EVERYTHING before you start any wiring. When you do wire something, make absolutely sure that the ciruit you made is doing its intended task (i.e.: O/P of each "head unit" is driving a set of speakers/power is connected ONLY to the Power I/P of each "head unit" antenna controller is acually heading to the antenna remote sense line)...nothing like driving a nice set of 200-Watt, Upteen-hundred dollars speakers with 5 Amps of 12 Volts DC to set your afternoon on fire!
It sounds like a "neat" project - I'd say about 2 afternoons (Preferably in an air-conditioned garage!!!) of about 5 hours each, just for the wiring alone and about 4 hours making up the panel, depending on where you're going to stick it and its related components...all in all, about 4 good days of straight work.
Good Luck! Hopefully, it won't drive you to drink!
