[rmcdonnell]

You have a poor (intermittent) connection as it sets over bumps.
It's unlikely to be the switch or relay, but could be the connections to them.
Unlikely to be the motor connections as it only fails in one direction.
Could be a duff wire, that has got pinched or nearly sheared somehow.
I vote for connection, so check them all, and remake them or clean them if possible.
Check for continuity if possible.

Best of luck
Russell