Please be careful on this. If you are unsure of what you actually have, get an electrician to check it out.
There are two usual methods of building a switched circuit (this applies to both lights and outlets):
- A home run to the switch itself, with that controlling whether any current passes to the light/outlet
- A home run to the light/outlet location, with a “switch leg” that controls whether hot gets passed to the light/outlet
In older configurations, the second option will have ONLY the hot! The hot leg comes to the switch; the switch breaks or completes the hot circuit to the fixture or outlet. The switch body is grounded, but the switch has no neutral. (I’ve seen instances where the ground is also nonexistent.) if the installer was sloppy, you’ll even see it done so badly that the wiring works as a “neutral switch” which is hazardous.
Test it, figure out exactly what’s going on with it before you try to change anything.