External lighting on a vehicle is regulated by the Federal government and can't legally be altered in any way.
That's a very reaching statement. It may be true in certain states, but I've "altered" busted modern truck, auto and trailer taillights by replacing them with DOT certified compliant lighting available at Wal-Mart and had nary a complaint about it from inspectors. It just has to match certain height, positioning, size, and brightness standards. Some were dog ugly like bolted on behind the busted OEM lights but they worked and they passed. :laughing:
Here's the law, 49 cfr 571.108 a.k.a.
FMVSS 108. I can't find a blanket prohibition about all external lighting, just a hefty list of standards compliance requirements:
http://cfr.vlex.com/vid/571-108-lamps-reflective-associated-19948537
Here's a more comprehensive list including Canada:
http://www.candlepowerforums.com/vb...-Laws-amp-Regulations-%95-Documents-amp-Links
The moderator over there is an expert who consults with the auto industry, and he often helps sort out issues of what's legal and what's not. While I stickler for the rules I've never heard him say all mods of existing external lighting was illegal, indeed he's taken a lot of time to help modders sort out what's allowed and what's not.