I'm trying to replace a 3 prong dryer cord with a 8 gauge wire. The control box has a three prong dryer wire that was originally connected to it. I don't have that type of outlet so I'd like to hook it directly to the 8 gauge wire which is already there and connected to a 50 amp breaker. My wire has a neutral but the wire I'm replacing did not. Not sure if I can cap the neutral, not hook either of them up. Stuck. Please help. Thanks
Electric dryers are typically designed to be protected by 30 ampere breakers, so I'm not sure why you would have a 50 ampere circuit. You'll want to check with the manufacturer to be sure what size overcurrent protection is required. If 30 ampere protection is required, you can simply swap the 50 amp breaker for a 30. Since the conductors are 8 AWG copper, there's no problem with using a 30 amp breaker instead of a 50.
A 3-prong dryer cord typically uses a NEMA 10-30 plug, which has two "hot" and one neutral prong. So I'm not sure why your setup wouldn't have a neutral.
3-prong dryer cords do not have a grounding prong. When using a 3-prong cord, the dryers chassis is bonded to the neutral via a bonding strip/wire. There should be instructions for this in the manufacturer's documentation, or on a label on the unit.
If you're running all new wire for this circuit, I'd recommend that you (or you may be required to) install four conductors instead of only three. This will allow you to have two "hot", a neutral, and a grounding conductor. You'll then follow the manufacturer's installation instructions for a 4-prong cord.
A 50A dryer circuit is running at 240V. You have two hot wires (each at 120V) coming out of that 50A breaker. One hot wire goes to one prong of the plug, and the other hot wire goes to the other prong of the plug. There is no neutral wire needed. The alternating 120V legs give the 240V. The ground wire goes to the ground prong.
You need the neutral wire when some component of a 240V appliance runs on 120V power, like clocks and lights on electric stoves do, and then you would have a four prong plug, the fourth prong for the neutral wire.