LH tail light wiring from electric control module
​​​​​Wiring Color Codes
N Brown
O Orange
B Black
S Slate
W White
L Light
K Pink
U Blue
G Green
P Purple
R Red
Y Yellow
BRD Braid
I would say, according the 1999 electric guide:
The seven wires:
3 Black/ yellow = Tail, Fog and Turn grounds
2 Orange/ yellow= Tail/Stop and Reverse/Fog/Turn 12V power
1 Green/ black = Reverse ground (pin 4)
1 Black/ orange = Stop ground

LH reverse light wire is BG (black/green)
RH reverse light wire is BR (black/red)

Parking aid gets juice from WR (white/red) that's connected to the Left Hand side reverse light ground wire BG. This is where I would put the connection.

If you don't need to connect directly to the light connector, consider (LH) Parking aid unit (pin 9) and (RH) Rear electronic control module for connecting. Peel the harness trunk side where you want the connection, if spare tire well is not a good place. Check also Rear electronic control module 17-way connector (ca63) pin 9. You might find both BG and WR wires there since the wiring don't actually change, the schematics do, along accessories.


Rear electronic control module pin arrangement

 

Now, the reduce it!