I am replacing a single pole switch with a new dimer switch. On the dimer there are four wires, rerd-black-blue and the ground. Where are all these wires connecting to. Jeff

The black wire should connect to the feed wire (the wire providing incoming power to the box - probably black), the blue wire should be connected to the load wire (the wire going out to the light fixture - probably black, possibly red), the red wire is unused - cap it off (it is only necessary for three-way switching), and the ground wire connects to (obviously) the other ground wires in the box.

Cheers,
Moishe