Discussion Forum - Northstar Chevelle Club

Not knowing the color codes by memory... but I'm thinkin' brown is the taillight circuit, and you should have a brown on both sides of the car.
Yellow is going to be "Stop/Turn", and it should be a different color on the other side of the car.

1st check would be the fusebox. Check for power on both sides of the "Stoplight" fuse.
Next check the stoplight switch that bears against the pedal. One side should be hot at all times, the other goes hot on brake application (plunger out).

Report back. The next steps get complicated, as it involves the turn signal switch & flasher circuit.

You are right on the colors  Mr. Delke.  Can the brake light switch be bad if brake lights work on pass side but not on drivers side .  I will check the fuse.  Then report back.

i put in new sockets.  Running lights work fine, does this mean ground is fine?  I took off all paint before putting in new sockets which are now very tight.   The yellow wire shows power when I use a test light and have Rachel apply the brakes or turn signal, but not sure it’s getting a full 12 volts.

-- Edited by jim larson on Thursday 20th of August 2026 09:46:17 AM

Brake lights will both come on if 1 side is hot, except that your black and white wires have been added in somewhere, as those are household colors/wires. Seems the left side white wire isn't getting power from wherever it is spliced into the line.

It appears that the sockets have been replaced at some time in the cars life with generic replacement sockets - hence the non-color-coded (GM correct) white & black wires in the back of the car. Make sure these non-OEM sockets have a good clean mechanical connection to ground/car body.

(My suggestions from here forward are based on my experiences with a '65. I'm pretty sure the color-codes are the same for '66.)

I'm bending toward a stuck/failing turn signal switch, or poor connections where it changes from wire to flat ribbon cable back to wire under the carpet (if they do that in '66... my '65 does). None of my wiring diagrams detail the turn signal switch... arggg.

After the brake light switch on the pedal, the "switched hot" (Orange??) for brake lights goes up the steering column into the turn signal switch. It does a few things in here:

- No signals engaged = "Switched Brake Hot" gets routed to both of the L & R "stop/turn" wires going back (L=BK/YL, R=Dk.G)
- Right Signal engaged = "Switched Brake Hot" stays made to the Left (BK/YL), and the Right (Dk.G) is broken. The flasher circuit is inserted into the Right side wiring.
- Left Signal engaged = "Switched Brake Hot" stays made to the Right (Dk.G), and the Left (BK/YL) is broken. The flasher circuit is inserted into the Left side wiring.

Check for +12v on the BK/YL & Dk.G wires (at the column connector) when the brakes are applied, and no turn signals engaged.
Check for +12v on the BK/YL & Dk.G wires (at the transition connector (wires to ribbon) near the fusebox/driver's footwell) when the brakes are applied, and no turn signals engaged.
Check for +12v on the BK/YL & Dk.G wires (at the column connector (ribbon to wires) in the trunk/backseat area) when the brakes are applied, and no turn signals engaged.

There's a breach somewhere in this circuit.

The Brown wire going rearward (and elsewhere) is your taillight circuit. It's connected to the headlight switch, and has nothing to do with brake lights or signals.

Jim, look at Americanautowire.com. they may have correct sockets for the car. As for the 2 wire socket, yes, it only passes the current onto the other side and you can tie another wire to it and have it work.
I have checked the notification box on this thread but am not getting notifications of replies...

Brake lights fixed and working.  Now I am on to the Nuetral saftey switch.  It doesn’t work correctly with my 200r4.  Thinking about putting in a switch for the TH350. THOUGHTS and advice .

https://www.ss396.com/chevelle/GNS-23.html

-- Edited by jim larson on Wednesday 26th of August 2026 09:12:24 AM