K10 will not close until the truck is activated. If you are getting C28 K10 will not close.
You will need to test the CAN bus lines from the traction amp to the display unit. J5-1 (CAN_HIGH), J5-8 (CAN_LOW) at the traction amp and A2-3 (GRN CAN_HIGH), A2-7 (WHT CAN_LOW) at the control head.
If can bus tests ok then I would suspect you have a failed traction amplifier.
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