any wire has a chance to arch.... if they are turned the wrong way so they are close to the headers or the block or whatever........ maybe they are old and broken too...
mine are awesome and they have 1,000 miles on them personnally i couldnt ask for much more qaulity in the product.........
well actually........they are hard to get all the grease marks off of but........lol
I ran FMS for a while they seemed ok but I wanted some thing different so I got Performance Dist. Live wires man what a diff. over the FMS not to mention they look way better but the car seems to idle and rev much easier. I've been think about some 50 ohm wires but haven't bought any yet.
IMO stay away from FMS wires they are not worth the money.
Probably the biggest factor is bendable boot ends,which helps keep the wires off the headers. And I never had any problem is another factor, but I think onefaststang said it best
I have always hated the FMS wires. They don't work for crap. MSD's are all I run. They advertise 50ohms per foot, and they are 50ohms per foot. I have tested mine and they check out. I have tested the FMS wires and some of them have checked in at over 300ohms per foot.
stock /ford style wires are great for stock ignitions, once you upgrade your ignition, you must get better wires.. taylor 409's are great, msd's are great, and livewires are great, all are made for hi energy ignitions...