2002 GMC Sonoma LIGHTS MALFUNCTIONING

I RECIENTLY HAD MY HEATER CORE REPLACED, AND RIGHT AFTER I PICKED UP MY TRUCK, I NOTICED A PROBLEM WITH THE LIGHTS.
THE HEADLIGHTS ALWAYS USED TO COME ON WHEN I START IT, AND THE RADIO ALWAYS USED TO SHUT OFF WHEN I OPEN THE DOOR.
NOW THE HEADLIGHTS CANNOT BE SHUT OFF WITH THE BYPASS BUTTON ON THE DASH LIGHT CONTROLLER, AND THE RADIO ONLY SHUTS OFF WHEN I OPEN THE PASSENGER DOOR. THE DOME LIGHTS CAN'T BE TURNED ON UNLESS I OPEN THE PASSENGER DOOR. THE SIGNAL LIGHTS STILL WORK.
I THOUGHT IT MIGHT BE THE SWITCH PANEL ON THE DASH, SO I REPLACED IT, BUT IT DIDN'T HELP. COULD THIS HAVE HAPPENED WHEN CHANGING THE HEATER CORE, OR IS THIS JUST A WILD COINCIDENCE? I DON'T WANT TO CALL THE REPAIR SHOP UNLESS THERE IS SOMETHING THEY COULD HAVE ACCIDENTALLY DISCONNECTED. CAN I DO IT MYSELF? WHAT CAN I TRY?
I CAN OPERATE THE TRUCK JUST FINE THIS WAY, BUT I DO MISS BEING ABLE TO SHUT THE HEADLIGHTS OFF WHEN I AM WARMING IT UP IN PARK. COME TO THINK OF IT, THEY USED TO SHUT OFF AUTOMATICALLY IN PARK, AND DON'T DO THAT ANYMORE EITHER. I AM ALSO CONCERNED THAT THE WHOLE THING WILL GO DOWN AND I WILL SUDDENLY HAVE NO HEADLIGHTS.
YOUR EXPERT ADVICE IS APPRECIATED.