When starting dryer,the dryer will only run as long as start switch is pressed.
I have tested all switches,replaced the motor,timer and thermistor,checked voltage.
And still the dryer will only operate as well as heat as long as you hold the start button in.
I have also visually inspected all connections as well as conducted continuity tests on most of the harness.
Here are your parts
http://www.appliancepartspros.com/parts-for-whirlpool-gew9878lw0.html
Have you checked the motor relay?
I believe that the motor and heat relays are the same.
Check the numbers on the relays just to be sure.
If the same swap the relays and see what happens.
If it now runs OK but does not have any heat then you need a new relay.
Yes I had done exactly that .
Sorry for not explaining that.
Is it possible the control board is shot?
Not sure what else it can be and I am becoming very interested in launching it into a dumpster.