ThanksEmerVehSolutions said:best guess would have to be because of the size of the lighthead...
Pimp said:I believe the old Whelen numbering system started with the size of the lighthead
52 series = 500 = 5x2
73 series = 700 = 7x3
44 series = 400 = 4x4
etc
EmerVehSolutions said:There is also a par 46