Huh? Which one & which car? A picture would help for sure. On my 70 all I can think of is the wire loom over the brake booster (reproduction available & not welded) & the welded-on firewall looms that hold the brake lines.

70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"