We have this issue on a few trucks, they are all newer F-250s with new steel caster electric spreaders. We have added work lights to the back of the spreaders and are having issues. Sometimes they don't work at all, sometimes they are very dim and the most common issue is they are on all the time, even when the truck is off and key is out. We decided to buy the fisher harness, part# 78381 and that has not changed anything. The one we are working on now is on a truck that has 200 miles and the spreader is also brand new, installed by a Fisher dealer. Harness is simple, red to red, black to black and the yellow harness wire to the gray module wire. What are we missing? It seems too simple. Waiting on a call back from Fisher but hoping to fix this soon. I can understand if something was installed wrong but this is happening to a few different trucks all installed by different people, one being the dealer. Any thoughts on what to try?