Electrical Problems?

Recently ive been having problems with flickering lights as well as stalling and electrical power loss throughout the truck. Yesterday someone hit my back rear fender and the problems ive been experiencing have increased greatly. The only way that the truck will turn over is if someone is sitting in the passenger seat. If i hit the passenger seat hard enough the entire truck will stall and will not start back up until the seat has pressure on it. everybody that has looked at the truck is confused and nobody can figure it out. Please help

 

check battery hasn't moved and is shorting to hood or fender or something

also check ground wires are still making good solid contact and I don't mean tight, I mean check them with a meter to ground

better check for frame damage as well if just sitting on the passenger seat affects something then the frame may have cracked and your losing ground connection