Plugs and Wires
They are illegal to run in some areas.
They are illegal ANYWHERE in the U.S. All this is under FCC jurisdiction, and I can assure you that it's highly illegal.
Now, I WILL admit that in the last 20-25 years, with the FCC becoming more politicized and less technosized, it might be an aging tiger with his teeth falling out, but it IS still illegal
Actually, new cars DO have to meet FCC interferance regulations, even though in some cases they can be "troublesome." Toyota, years ago, was particularly non cooperative. Very common, with vehicles and two-way installations.........to see additional supression measures, groundindg / bonding on hood, doors, exhaust etc and additional filtering here and there
When I had my Mom and Dad's 86 Dodge 600 (K car) after Dad died, I was still active on amateur radio VHF / UHF. The damn EFI system in that car had a substantial "birdie" right in the middle of the 2- meter amateur band. I think it was 146.52 MHZ which is supposed to be the "national calling frequency." So naturally, I had it in the "scan list" of the radio.
A very quick look with an r.f. spectrum analyzer will show just how dirty some of this stuff really is.