Question on turn signals

both my turn signals work( 69 Dart) has column shift steering column.
However the left one, if you bump it just a tiny bit the turn signal lamp acts spazzy( barely on, etc) but if you hold it in the center all is good, if you pull it down to make a turn all is good.
Just seems loose/ sloppy in the middle and with big camshaft and radical idle it sometimes is so sensitive it as i said above acts like its between the on/ off position
What needs replaced?