Check the plug at the light for corrosion. If none, I suggest seeing if the bus will provide enough amps to operate a sealed beam headlight bulb. If so, blame China for yet another high quality Soundoff/Otilux light!
Thanks for the info Thomasbus 24. that was the first thing we did was check the connections. Found the backup light relay in the electrical panel had a loose connector recrimped the connector now all is good.