Brake lights, blinkers, cruise don’t work when towing camper w/ headlights on

What is your question?

All lights work fine, as does the cruise, on van and camper until I turn on the headlights. I lose the use of cruise control, the blinker lights become flashers on both vehicles, the brake lights don’t work at all, when I brake the dashboard lights go off and come back on when I release the brake pedal, and the compass and temperature display are not visible.

How long has your 2002 GMC Safari had this problem?

Since I purchased the car 10/10/18