Connector acting as ground?
The 78xx is a linear regulator, which means among other things, that its power dissipation is directly proportional to the load current. A heatsink is required to keep its temperature within an acceptable range.

How much current does your load draw?

Also, @Phil G raised an important point: if you're mounting your banana jack to a metal panel, the panel must go between the two plastic insulators, with a clearance hole that's large enough to acommodate the positioning shoulder(s) on them.