What's the purple wire?

[Steve83]

I can't find it in any of the wiring diagrams (I checked '72-77), and the harness is not only crispy from age, but also painted, so I don't want to try to dig into it. There are too many other take-outs at this location, anyway.

But it's a single plain purple wire directly under the middle of the dash, behind the BRAKE light (which has both its wires) & cigar socket (converted to USB power) going to a single black quick connect, in a '74 with factory wiring. My 12V test light shows no voltage in any key position.





I'm sure I'm missing something obvious...

 

[Jfryjfry]

Is it 977 At c242? It would be the power wire for the brake light lamp off of the ignition. Your diagram shows purple with white but the 72 shows a solid purple.

 

[Steve83]

I don't think so, but I'll re-check. I can't see the brake light even with the phone camera, but I could feel 2 wires connected to it.

 

[Quick & Dirty]

Is it 977 At c242? It would be the power wire for the brake light lamp off of the ignition. Your diagram shows purple with white but the 72 shows a solid purple.

This. The connector hanging goes to the ignition switch. The wire goes out to the engine bay harness then comes back to the brake warning light. The light is powered from the ignition circuit through the red/yellow wire. The ignition switch grounds the purple wire during start so you can check the bulb function. The warning switch will ground if there is a pressure imbalance between the 2 brake circuits.

From my '74 dash. The wire is solid purple;

 

[Steve83]

I think you're both right - I managed to get some pics, but none that showed that side of the ig.sw. I'll check there specifically next time I'm in the shop.

 

[Steve83]

Yes, that was it. Thanks to both of you. Turns out I was able to see that terminal through the steering column hole.

Unfortunately, the light still doesn't prove out during cranking, but that's not one of the owner's concerns right now. It got 32" tires and an alignment today, and it's getting exhaust next.

 

[Jfryjfry]

It could be the switch is stuck (in the brake “block”). I have heard about how it can be difficult to get it to find it’s happy place in the middle.

 

[Steve83]

That would keep the light ON all the time.

 

[Rustytruck]

Not if the bulb is defective or burned out.

 

[Steve83]

That's my point - the balance switch being off-center could never be the cause of the light NOT proving out.

But again: the owner doesn't care about the brake warning light right now.