Is it a plastic prong sealed together
The 3rd round plug is the ground connection.
Yes, provided that you have a ground wire in the box and that the ground wire is properly connected in the electric panel.
On a three prong plug there will be a neutral blade, a "hot" blade and a ground blade. The neutral blade is wider that the "hot" blade. In North America the ground blade is "U" shaped.
Need to know the amperage rating of the plug or the NEMA configuration of the plug and receptacle
My question is WHY did you replace a four prong dryer plug with a three prong! 220 volt Electric dryers require two hot legs, a neutral and a system ground wire. Sounds as though you shunted one of the hots or the neutral. You need to install a four prong plug of the same configuration and wire it exactly as the original.
Yes, provided the outlet has a three element receptacle. The third prong is ground. If you use an adapter that connects three prongs to a two slot outlet there is a shock danger.
If you are in north America, black and red go to the main prongs and white to the ground (round prong) . Black and red can be on either main prong.
The AC wide prong is the neutral. An AC voltmeter measuring from narrow prong to ground should show line voltage; measurement from wide prong to ground should show zero. In a two-conductor power cord (and some three-conductor cords), the ridged side should be the neutral. In any light-bulb socket, the outer ridge should be wired to neutral.
It may be a 220 Dryer, and you will need a new outlet installed. There should be no extra wires when connecting the Power cord to the plug
Sure i do
The auto parts store has given you the wrong headlight. Take it back and exchange it for the correct one. Take the old one in so they can see the correct one that you need.
You should install a four prong. The older ones were three prong and had no ground. An adaptor isn't made because it wouldn't fix the problem. You could make your own adaptor and cut the ground off with a pair of dykes, but don't.