Wiring for side marker lights on 82 VW Golf Cabrio (Rabbit Convertible)

Hi, my brother is restoring an 82 VW Golf Cabrio (Rabbit Convertible).  He has side marker lamps to install in the fenders/wings, but isn't sure where they plug in?

I've attached some photos–would anyone be able to advise?

Thanks!

Tony

The rears plug in to the tail lights left and right side.

The fronts
Follow the turn lamp wires,
left front
black /grey meets the parking light (turn) grey at the junction of the grey/black feed

right front
black/grey meets the grey from the parking light(turn) ties in to a red/grey feed.

Thank you Briano, and apologies for my delayed reply!  Your advice was hugely helpful and it looks like my brother has gotten the rear lights sorted now.  Thank you!