Driving behind my wife who was in my 68 cutlass holiday coupe i noticed that when she was braking the brake lights were on, but as soon as she put on the turn signal the brake light on the opposite side stopped working.

Any ideas on what to check first?

 

Likely a bad ground connection. Follow the harness in the trunk from the lights working toward the front of the car, clean and tighten any ground connections. Remove the bulbs, clean and tighten connections/contacts.

 

I don't think this one is a ground issue. The brake and turn signal circuits use the same filament in the 1157 bulb. If the ground were bad, it would show up when the tail lights were on or off, not the turn signals.

The only place where the turn signals could effect the brake light on the OTHER side is in the turn signal switch. Since the brake and turn lights use the same filaments and the same wires to the back bumper, the turn signal switch has contacts that switch these wires from the brake light switch to the turn signal flasher when you put the turn signals on. The other side is not supposed to switch, but if the contacts inside the turn signal switch are bad or if the plastic parts of the switch are broken, it can cause this problem.

 

Joe I have the same issue on the 64 F-85 build-tail lights work turn signals work, no brake lights. Thanks for the heads up. I will order a new turn signal switch.....

 

Rob if your tail and TS's work, and no brake lights I'd be more suspect of the brake light switch.

 

Agreed. The OP has the problem of the brake lights work UNLESS the turn signal is on. That is different from no brake lights at all. In Rob's case, I'd check for power coming from the brake light switch before replacing anything.

 

I have power ( to) the brake light switch. ( I'm using a later GM brake light/cruise control switch I bought new) The cruise control switch is wired to my 200-4R to unlock the converter when I touch the brake. Like a lot of us I have bought new defective parts. Will have to look into further-thanks

 

Do you have power out of the brake light switch when the pedal is pressed?

 

I will get out there and check it, but i think you solved my problem...

 

 

Haven't had a chance to look at this yet, but I suspect you are correct here. My son, who was driving the car the other day said that the left turn signal no longer flashes. I will order a new turn signal switch.

 

OK, I have my new turn signal switch and wiring and I have the steering wheel pulled, but I can't seem to find a steering wheel lock plate removal tool that fits my 1/2" threaded steering column! Everything out there is for a 9/16" thread! Anyone know where to find the proper tool?

 

All the ones I've ever seen come with both sizes.

 

All of these tools come with a 9/16" thread and a metric thread.