Some are linked as you say - I will give you a diagram for the socket wiring - see the attachment.
What you then need to do to wire that / the other end to the car is , use a 12v test lamp or meter - Switch on one circuit at a time - ie, lights - indicators, brake lights etc as you go... but one at a time.. and then probe each wire / connector to the lamp to find the then live circuit - once you have identified that with the tester / meter - wire the associated colour wire to that one / connector / wire . ( usually using blue scotchlock connectors onto the relevent wire/s.
Let me know how you go..and / or let me know if you need anything further on this..~>>~~>>~ Meanwhile now at this point- Please do click on the "Exc / Ok rating" for me at this time.. "Thank you" in advance for that ... Note that you can get back to me anytime at all after doing the rating - it doesn't close you out -- Best Rgds, MIKE