Went back to the customer yesterday and did some more troubleshooting, as I am always reluctant to replace the oscillator card since the are very rarely the problem.

Upon further investigation I found that the contactor was indeed getting a negative from the boards, but the positive from the driver board was on occasion dropping out and or not carrying appropriate amperage to pull the contactor in. I jumped across the board (direct from the brake switch input to the contactor output) and bingo the truck started working.

This isn't the first time I have had this type of problem with one of these driver boards.

And correct when attempting to operate the truck the display was showing a blank screen as if the truck should be operating.