Replacing light switch with dimmer - can't identify wire colours; no ground

Question

I'm trying to do a straight replacement of a single pole light switch from a regular rocker switch to a dimmer.

I pulled the old switch out of the box and found the following:

• two wires coming out of the top, one red and one blue. I can't find anything online that tells me which of these wires is which so I'm not sure which one to attach as hot in the new switch.

• there isn't a ground wire. I've read that the switch will be grounded just by attaching it to the metal box, but is this true? Should I attach a ground wire to the box?

I'm in Canada, if that helps. It's an older apartment too (which may explain the lack of ground wire?)

Answer 1

Most likely, it makes no difference if you're installing a simple dimmer switch. All a single pole switch does (even a dimmer) is interrupt a hot circuit. If your switch installation instructions call for specific connections (i.e hot must be hot, switch leg must be switch leg), then use an electrical tester to determine the hot lead.