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.

Sounds like the reverse light switch for the manual transmission. Are the wires green?

The wires are blue and dark blue, almost black. I never thought it might be for back up switch, I do have a manual trans, the bracket is there but no switch. The wires will reach. I need a switch anyway, will see if the wires plug in.
Thanks

"Goes through firewall near steering".

Does it go through a standard firewall breach or does it look like an aftermarket hole? Pretty easy to tell if it was done after it came out of the factory. The breach in the wall would be isolated or have that semi-pro appearance to the hole and grommet.

Are the wires bundled professionally to others as it passes through the firewall? These observations can help determine what the wires were meant for.

It goes thru a factory breach, the wire is all by itself, no other wires go thru there. to be more precise. it goes thru firewall close to brake booster, about 1 inch away from top bolt that holds booster on. between that bolt and wiring thingy where your harness starts. Also I noticed there is another wire going thru firewall directly below this mystery wire, that wire goes to a 30 amp breaker on firewall and from there goes to horn relay.

I don't see the "mystery wire" on my '68 in the position you mention. That second wire (breaker to horn relay) is probably the power top circuit (also for power windows).

I just had a look at mine and i do not have the mystery wire you mention, nor the factory breach in the location you referred to.

David

Jim brings up a good point... (haven't looked at the color code, so just guessing and running with Jim's idea) do you have the wires on the breaker that is on the firewall, just abover the brake booster (between that and the wiper motor) It has two studs on it, and as Jim mentioned is for the power top and power windows.

Brett - 67 Drop Top 455!

Yes, Jim and Brett are correct, mine has the same. It is for the convertible top.

Johnny Mac
http://my67.net

Mine has two holes also, but I only know that one is for the power accessory feed. I still haven't figured out what, if anything the other hole is for.