Ford Bronco not starting

I have a 1996 Ford Bronco XL and every time I go
to start it, it just clicks and shuts off. Whenever I
turn the key to the on position, all electrical
components come on; lights, gages, radio, etc. but
when you turn the key to start it all you can hear is
a loud click in the engine bay, and everything shuts
off. After that I have to get out and wiggle the
battery cables for all components to come back on
and it just does the same thing. It’s got a fully
charged battery in it. Any help is wanted. Thanks in
advance!