1998 DeVille. The left rear brake light does not illuminate when the pedal is pressed. The right side & center window light work fine. But the blinker & hazard flashers, which use the same filament, work. Bulb is ruled out as possible cause. I swapped left & right bulbs, and problem stayed on left.

So somewhere there must be some logic that combines the signals from the brake switch, blinker switch, hazard switch, and blinker/hazard oscillator into the signal sent down that yellow wire to the bulb. It is so hard to find and track wires, does anyone know where to look?

I see four wires coming out of the blinker lever switch itself. None are yellow (they are white pink purple & green). I'm not sure how to access the back side of the hazard switch, another likely place where the logic might live. On the surface, that does not look easy - would involve a disassembly of the steering column.

Thanks in advance for any help!
Lonnie

 

The problem is not with logic, or even with the brake switch because the other two brake lights work. The problem is with the circuit. It could be either on the ground or battery positive side of the circuit.

It is easy to test wiring with a multimeter, but you can use a bulb and two pieces of wire to locate the problem. Tape each wire so it makes contact with one pole on the bulb, then use the other ends of the wire to probe the circuit. Start here:

1. Test the ground circuit by connecting the bulb to the battery positive and the ground conductor at the tail light bulb socket.
2. Test the battery positive circuit in a similar manner from the battery negative to the brakelight conductor in the left lamp socket.

You can continue with similar tests to those listed above to find the exact location of the break in the circuit. Once you find out if it is on the positive or negative side of the circuit, work from the bulb out to locate the break.

The positive conductor for the left brake light comes from the stoplamp switch and goes thru a splice connection where it splits into the three wires for the right, left, and center bulbs.

The negative conductor comes from a ground connection and passes thru a splice connection.

Both conductors pass thru a connector in the trunk near the tail lamp. A bad connection at this connector is the most likely suspect. Otherwise check the ground connection and splice connections.

 

There are 4 wires that emerge from a hole in the chassis at the rear, which supply a signal to the brake lights:
* Black: ground (neg)
* Brown: Tail lights (when head lights are on)
* Green: Right brake & blinker & hazard
* Yellow: Left brake & blinker & hazard

All four wires are good. There is no break in a wire or bad connector or bad splice connection. It is the signal on the yellow wire that is faulty, but the wire itself is fine. When the left blinker is on, or hazard is on, the yellow wire is carrying a pulsing 0..12V..0..12V..0.. signal, and the bulb illuminates in that case. But, when the brake pedal is pressed, the signal on the yellow wire is not there as it should be.

The green wire is the right-side dual of the yellow wire, and it works perfectly. Thus, the right-side brake light does work.

After working on this for most of the day, I am now convinced that the other end of that yellow wire must terminate within the steering column, probably on the blinker switch itself. The "common" terminal of the switch would be this yellow wire, the "off" terminal would connect to the wire from the brake pedal, and the "on" terminal to blinker oscillator. That would be consistent with how the brake and blinker share this wire. I.e., when the blinker lever is not on, the brake pedal switch is connected directly to the bulb, but when the level is on, the flasher is connected instead.

That seems to leave two possibilities. (a) The blinker switch is bad, or (b) the wire from the brake pedal to the blinker switch is severed. However, since the right rear brake bulb lights up, it appears (b) can be eliminated (assuming there is a single wire from the brake pedal).

So now for the past several frustrating hours, I've been trying unsuccessfully to remove the steering wheel in order to get access to that blinker switch. I've put a puller on there and screwed it down so tight that the end of the steering column bolt is starting to deform. It is pressed on there so tight,
I'm at a loss for what to try next. (Just in case your thinking it, yes I did remove the center nut :-) ).

Are there any tricks of the trade for pulling a stubborn steering wheel like this?

Lonnie

 

Problem solved. It was indeed a worn out blinker switch. The copper had worn down to where there was no copper remaining on the contact that the yellow wire connects to. I've ordered a new blinker switch on-line ($57.30 after tax & ship).

The steering wheel removal just took a huge torque on the puller. To protect the end of the column, I put a piece of 1/8" steel. The compression was so great that it had flattened the center of that piece to zip & punched a hole through it. That was one steering wheel that didn't want to come off!

My problem solved for now. No need for further replies. Maybe this will help someone with the same problem in the future.