'57 Pontiac Wiring Route
 

Hi All,

I have '57 Pontiac SuperChief and I trying to re-run the wiring harness (which was removed when the car was torn down years ago). I'm trying to figure out which wires go through which holes in the firewall and how they are routed. Does anyone happen to have a diagram or pic of the interior firewall to show how wires are running. I have a shop manual but there are no routing instructions, only the electrical schematics.

Dave

See attached for wiring pics from my 57 StarChief convertible, which may differ slightly from the SuperChief. Sorry for the poor quality, but its a tough area to get to with the car in storage.

I've also included 57 wiring diagram and a 55 body layout diagram.

This colored coded diagram may also be of use:
https://classiccarwiring.com/product...wiring-diagram

@peters23 Thank you for the photos and the diagrams. Any chance you can take a picture of the drives side firewall from the engine bay so I can see which holes the wires run through? Also, where did you mount your fuse box. It's a bit difficult to see where it is actually mounted from the pic? This really helps. Thanks.

My car is a (mostly) original, America manufactured Pontiac. Fuse box is mounted on left side of steering column, when viewed from inside.
If your car is a Canada manufactured Pontiac, it may be using Chevy wiring, as Canada models were largely based on the Chevy chassis, and used the Chevy engine.
If that is the case the above information and pics probably will not apply to you.
What engine is in your Pontiac?

@peters23 My car is American also - from Texas. It is not a Canadian car. I had to swap my engine for a '55 287. My original 57 motor was fully seized. I know that the fuse box is mounted to the left of the steering column, but I can't figure out which mounting hole to use. I also have two rectangular openings in my firewall on the drivers side. I've fished my harness through the larger opening since it was the only one that would allow the fuse box to go through.

Here are some better pics.
I had to take a plate/cover off next to the fuse panel.
There appears to be another plate/cover on the engine compartment side, but everything is covered in tar.
Its a bit complicated as there are branches on either side of the firewall that seem to intermingle (The "Aux" section might be sensors going back to dash?)

@peters23. Thank you so much for these pics. Definitely help me out. I'm going to send you some pics later today with a few questions. You are a rockstar my friend.

This photo shows the backside of the fuse panel that I'm holding. It shows how the fuse panel is attached to the cardboard on firewall under the dash. The left end clips into a slot on the cardboard and the right side gets screwed down. This is 56 but same as 57.

@Safari Larry There's a cardboard panel that attaches to the firewall. Well, ****! That piece didn't come with the car. Guess I have to fabricate something. Any chance I can get a pic of that cardboard piece and how it sits under there?

It is available at CPR, see https://www.pontiacparts.net/product/1957-firewall-pad/

@Safari Larry . Wow! $354 USD for a piece of cardboard. I may have to figure something else out. I would still love to see how it looks under the dash.

Yes, does seem expensive. It has the proper cutouts and insulation on backside plus plastic trim sewn onto bottom. Maybe someone has a photo of it. Your choice.

@peters23 I've taken a picture that shows three parts in my wiring harness. I have no idea what they are or where they should be mounted. Maybe you can help me out?

https://i.postimg.cc/RCw0zpp3/20250611-195129.jpg

Lower right could be the horn relay, but colors don't match factory brown, red and black.

The lower left could be the neutral safety and backup light switch, but would need a bracket that I don't see to attach to the steering column. Wiring diagram shows black, red and brown wires, which does not match yours and shows a 4 terminal switch. I guess a manual transmission car could have a 3 wire switch.

The upper left switch is likely a brake light switch, but I can't find a drawing of it in the 1960 Master Parts Catalog. Wiring diagram for 57 Pontiac shows one side of the switch has a pink/black wire like your pictures shows. Diagram does not show wire color on the other terminal.

Diagram can be found here. https://www.oldcarmanualproject.com/...re5765-328.jpg

See below for a few more clues.
The switches with the linkages don't seem to match what I am seeing on my car, which has power brakes and automatic transmission.
If yours is manual transmission and/or manual brake it might be different.

The upper left is brake light switch for manual brakes (not power brakes). It attaches to the firewall with lever going over the brake arm. I'll see if I can get a pic of it.

Here is photo of the brake switch next to the brake pedal arm. View is looking up from under the car. Also, photo of the neutral safety switch attached to the steering column. These are photos from my '56 but these switches are same as 57.

Tip for Dave: include photos as attachments rather than link, it might be easier for you. You need to select "Go Advanced" in your message to get the Attachment link. Then select the paper clip (Attachments) icon. Choose the file, then "Upload". After attaching files, select "Preview Post" to see that the message looks the way you want it with attachments showing.

@peters23. Thank you for the pics. They really help out. And thanks for the tip about attaching pics. I will certainly do that going forward.

Peters23 sent a good photo of the Neutral Safety Switch from the top side. In the photo of the brake light switch I sent, if you look up at the steering column next to firewall, you can see a bottom view of the Neutral Safety Switch. I cut out that portion of the view and added some description to it, see attached.