As far as I know, you do need a permit in NJ to run an amber light. I'm not sure where to get it, though I know the DOT has to issue it. I found this out from a friend who went to annual State motor vehicle inspection. They asked him where his permit was for his permanently mounted light.
I would imagine that it's a cheap fee like the $7 others mentioned.
My amber lights are magnetic mount, and so is my brother's. We only have them on when actively plowing. We NEVER use them when transporting from job to job on roads.
That may be a key here. If the truck is in a lot, plowing, then the police can't issue a summons. That would be like them issuing a summons for plowing with a back hoe, with no liscense plates on it. If it's not on the road, they can't do much. Now if you plan to plow roadways, then you should get the permit. If it was easier to find out how and where to get one in NJ, I'd get one myself. Occassionally I park my truck curbside with the amber lights and hazzard flashers on, when we are clearing sidewalks. This is to alert traffic that we are working there. Then again, I sometimes drop a few cones behind my truck as well. I wonder if I need a permit to use cones on a road?
I do it for safety sake. I also wear a reflective orange vest when doing walks close to the curb.
Amber lights are typically used to alert other drivers of a safety concern. Tow trucks all use them. Maybe you could ask a tow truck owner where and if he has a permit for his amber light? Red and blue lights are for emergency vehicles only. If it's not a municipal vehicle, or volunteer fire fighter's vehicle, you can't run them at all.
~Chuck