I'm restoring a 68 firebird convertible, going together nicely, do have one wire underwood unaccounted for.I know it's not for a voltage regulator or horn relay or horn. this wire originates at key switch, goes thru firewall near steering column and goes to radiator support and I remember it plugs into something. any idea what it is ? it has 2 plugs, like maybe one is positive and maybe neg. My 69 hardtop doesn't have this. I wish I would've saved whatever it plugged into, never dreamed I'd be restoring this car years later. wiring diag doesn't show this mystery wire. I think it does have something to do with being a convertible.