Changing a 3 pin connecter to a 4 pin.

I want to change one of my fans from a 3 pin connecter with rpm monitoring to a 4 pin connecter ans still keep the rpm monitoring. If I cut the red and black wires from the 3 pin connecter and change them over to a standard 4 pin connector, will the rpm monitoring still work? Does the yellow cable need a ground wire to work?

Also, can I just pull out the cut wires from the 3 pin connector so I don't have live wires in my case?

U could just get one of those 3 to 4 pin adapters with rpm sensing