I am trying to change the light switches in my apartment. I found out after taking out the old switch, that there is no ground but there were 3 separate black wires coming from the box. I changed the old to the new switch, but since there were 3 black cables coming out, I only back mounted 2 of the black wires to the switch. The other one I capped off. Now, the 2 elextrical outlets on that same circuit from the fuse box do not work. The light switch does work though and turns on and off the fixture that it is supposed to control.

Should I side mount the extra 3rd black cable? Can you side mount and back mount at the same time? Don't understand why there are 3 cables and how that would affect the electrical outlets.

Thanks in advance.

Since the outlet worked before, and now does not, the capped off wire must be feeding the outlets. Need to connect it back to the hot wire feeding the switch.

Backwireing a device is not as good as a splice or a screw terminal, but cannot put two wires under a screw, and the backwire method is popular cause of loose connections. Both be done at the same time, but you risk having problems later.

Better to splice with wirenuts.

Keep in mind, you should not be doing electrical work in a building you don't own, and other tenants/occupants can be affected by any problem you may cause.

It could be a 3-Way switch. It there another switch that controls the same light as the switch you replaced? Do you still have the switch you replaced? Were there 3 terminal on it? If so it's a 3-way!