I just recently moved into a home that was built in 1978 and it has a 3 prong plug for the dryer and my dryer has a 4 cord plug. How can I convert it over?
You can just by a three prong plug. Take off the old plug at the terminal block, and get the three prong plug. and it will have there wires to it. Put the middle wire on the middle terminal of the terminal block on the dryer, and the other two on each end. Tom ApplianceEducator.com
When replacing the line cord.
You should also add a ground strap from the center terminal strip wire (Neutral / white) to the frame. Often it is there just not connected.
Without this the units frame is not grounded and could go live which is very dangerous.
Get your Model Number and check the Whirlpool appliance website you should be able to find install instructions there.
This may also help
http://www.applianceaid.com/electrical_testing_tips.html
Just saw this in one of sidfink43’s posts
American A/C & Appliance