I suspect the input jack itself... if it's a 'barrel' type like on thousands of basses out there, the contacts are HALF the size of a standard 'open' Switchcraft type jack. It's stereo, meaning the other 'hot' terminal is actually used as a battery ground- completing the circuit, and turning on the battery. That's why the battery runs down if you forget to unplug the bass. That part is usually the first thing to fail on a bass equipped with them.
P.S., I'm a professional repairman in Reno, Nevada. It shouldn't cost you anything, or very little to have a tech look at it.