Maybe this might help.
RC51 wiring <-------------> Hotbodies undertail
Brake lights = Grn/Yel <----> Red
Tail lights = Bl/Brn <-------> Blu
Ground = Grn <------------> Blk
Left rear signal = Org <----> Org (one for each signal)
Ground = Grn Same ground used on undertail
Right rear signal = Lb (light blu) <---> Org (one for each signal)
Ground = Grn Same ground used on undertail
License plate light = Bl/Blk <-----> Separate light not part of undertail
Ground = Grn
All rear brake/running/signal/license lights essentially connect to same ground point on wiring harness.