I agree with micky.
99% of the time it's a jiggly conection on one of the 2 conectors on the logic card.

Hate those things....

try opening the logic unit and checking where the pins are soldered to the card you get cracks in the joints very common.

Hi ben g.I worked a on a unit that the electrcial panel was my in germany and found a diode block in line with both contactors, which cause all shorts of problem.

Hi ben g
The problem is most probably the power unit, either one of the power devices has failed (thyristors or capacitors) or more likely the logic in the power unit has failed. The reason why you are getting battery voltage on both sides of the direction contactors is that the contactors have a common positive from the key switch and a negative for the contactors comes from a safety relay in the power unit logic. The relay supplies a negative feed to the foot pedal micro switch from there to the direction switch and then to the forward or reverse coil. If the truck faults the relay opens and removes the negative feed, so you will measure battery voltage on both sides of the direction coils.
Shane

The truck lurches then cuts out contactors will not pull in and then when you check the contactor coils you have batt volts to both sides again.

Hi ben g
Most of the time the problem is the small black logic mounted in the 4849 power unit (2 aluminium heat sinks with the power components mounted between them), also the switches in the Bosch foot pedal used by Clark sometimes fail.
Dos the truck lurch and fail to safe or just drop out the direction contactors?
Shane