I have seen folks argue with this but there are basicaly two different types of towed light systems. One uses the main "Service" lamps activated via a diode pack that is often under the dash. the other is used different bulbs for towing and driving..
The brake light switch (Which is usually under the dash) has two leads. one is "hot" (12 volt battery side of ignation switch) only thing between it and the battery is a fuse.
The other side is switched (Goes to the diode pack if you have one via the turn signal switch OR to the brake lights via the turn signal switch)
Tap this wire.
lay an LED assembly on the dash (Secure it)
Where your Back Up cam can see it clearly.
OPtion 2:
Upgrade the flat 4 or 6 pin connector to a 7 use the additional pin