My lights, mounted on the aftermarket bumper, were real dim so made up some beefy straps to go between the frame and the bumper, the battery and the frame, the frame and the tank and the frame and the front fenders for the front lights.
Even though there likely was some sort of connection through bolts and hardware, the ground connections were likely of fairly high resistance. The straps make sure of a good connection.
I also slobbered some fluid film on all these connections, to keep the corrosion at bay.
The lights burn my eyeballs out now and my gas gauge, previously pointing to empty, also came back to life.