When changing a 4-prong to a 3-prong cord does it matter that the 4-prong has a ground wire and the 3-prong doesn't?

Answer for USA, Canada and countries running a 60 Hz supply service.

Yes it does matter. You should be upgrading your electrical system not downgrading it. Leave the four blade plug on the equipment and change the wall receptacle to a four blade receptacle. Ground the green terminal on the receptacle to the receptacles junction box. Tucked away in the back of the box you should see a ground screw, connect a jumper wire from this terminal to the new receptacle.

If you don't see a ground wire in the junction box, the electrical code states that a ground wire should be taken from this junction box back to the electrical distribution panel and ground this wire to the ground bus in the panel or to the panel's metallic enclosure.

As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.