Someone please help me! I replaced the fuel sending unit and the guage worked, hit a bump and it shot up to full(it really was empty). Any suggestions? Where is this unit grounded at?

To add a ground just drill a small hole way out at the corner,past the seam weld,and same on the frame.Add a ground wire with 2 eylets on each end and screw it down.New ground.It won't care where it's grounded.

To add a ground just drill a small hole way out at the corner,past the seam weld,and same on the frame.Add a ground wire with 2 eylets on each end and screw it down.New ground.It won't care where it's grounded.
Exactly where should this be done? also could this be the problem?