I know this post is quite old but here goes ignore the batteries I assume the truck is a geny start model so go for the basics and work up ,set up the potentiometers on the foot pedal and lift. should be 4.2 -5 volts at rest depending on model up to 8.5- 9 on full stroke. However the most likely cause is either tachogen in end of motor or current censor in the cable between motor and gen.Hope this helps