I believe you are working on a ev100controller if so you need to get a GE hand set and plug in the center port the plug that you take out will control the dash when you plug in you will have no dash display the controller will give you a number like -23 than you can try to fix truck without that it is very difficult it could be any part in the system that can cause that.the six screws that you are testing are just inputs screw 5 and 6are forward and reverse that means your switches are good and wiring to switching to controller but you can't check outputs the hand set will help with this hope l was of some help