That's a Whelen model 6000 bar and it is ultra rare to find. It is to a Whelen collector what an Aurora Borealis is to a Mars collector.
I had the nicer model 6029 all strobe bar back in the late 80s that I obtained from a wrecker owner in a swap I initially hesitated to make for an Edge lightbar. At the time, I didn't really want it because it was not widely used because not many of them were ever made and Edge bars were very popular and all the rage. The 6000 was considered very ugly and bulky and it was hard to access the innards because of the long single piece dome, which was very thin and flexible. The model 8000/80/90 series bars with a better dome setup came along soon after it was introduced in the mid 70s and made it obsolete. The one I got had a clear dome, which was unusual to see on any type of lightbar at the time, and I liked the fact the inner colors could be easily changed and that's the biggest reason I made the swap for it. I had no idea it would ever be collectable or I would have taken much better care of it, as it fell off a rickety shelving rack in my garage shortly after I got it. The single piece clear dome literally shattered into several pieces, and I still kick myself for not having it secured on a more stable surface better. I still have one of the power supplies from it, and the metal speaker grille that fit on the front of the dome is around here somewhere. I've only seen one other model 6000, which was several years ago while on a trip, and it was on an abandoned fire truck in a pasture and almost half of it's red dome was cracked/broken/missing.