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1966 Coupe restomod
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Discussion Starter #1
Do the rear brake lights and turn signals share the same bulbs? My left rear brake light isn't working (i.e. wont light up when I press the brakes) but both turn signals work. Trying to figure out if it's the bulb or possible wiring issue.
 

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Do the rear brake lights and turn signals share the same bulbs? My left rear brake light isn't working (i.e. wont light up when I press the brakes) but both turn signals work. Trying to figure out if it's the bulb or possible wiring issue.
Yes, same bulb #1157. And it's the bulb.
 

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Discussion Starter #3
If they share the same bulb, then wouldn't it be a wiring issue? Pressing the brake pedal wont light the bulb but the turn signal works.
 

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So would that mean it's likely a wiring issue?
Yes, or the brake light switch. Early Mustangs had a pressure switch on the master cylinder. That was changed to a switch on the brake pedal. I do not know exactly when they went to the brake pedal switch but it was fairly early. Someone else will know for sure.
 

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So the brake pedal lights up the right light but not the left.
That means there is power and the switch works.
Could be a wiring problem to the left light.
Turn signals light up the same element that the brake doesn't.
Hmmm that means the wires from the turn signal switch are working.
Your problem is in the turn signal switch.
 

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1966 Coupe restomod
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Discussion Starter #10
So the brake pedal lights up the right light but not the left.
That means there is power and the switch works.
Could be a wiring problem to the left light.
Turn signals light up the same element that the brake doesn't.
Hmmm that means the wires from the turn signal switch are working.
Your problem is in the turn signal switch.
Thanks Asm109!
 

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Discussion Starter #11
Its odd...it was working a week or so ago. I wonder if it's something I did. I was messing with the fuses the other day to troubleshoot another problem, and I accidentally put the headlight fuse (30 amps) into the socket twice while the light switch was pulled out (in the on position), which caused a mini spark. Could that have done it?
 

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the headlight fuse (30 amps) into the socket twice while the light switch was pulled out (in the on position), which caused a mini spark.
What are you working on? A standard Ford has no headlight fuse as it's a circuit breaker built into the headlight switch.
As Asm109 said, the problem is your turn signal switch. And don't replace it with an aftermarket switch as they are known to be poor quality. Find and pay big bucks for an NOS Ford switch.
 

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Discussion Starter #13
I was working on locating a parasitic drain. My car had a headlight fuse. I assume I have to disassemble the steering wheel to get to the turn signal switch?
749161
 

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Once you pull the steering wheel off you'll see the turn signal switch right under it.

What year is your car? If it's a 67/68 try playing with the hazard light switch first before you start pulling things apart. Sometimes they can get stuck halfway on and they do weird things.

Also, that's a fancy looking aftermarket fuse box you've got there. If someone rewired the car there's no telling what kind of things they may have changed.
 

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Discussion Starter #15
Ya, I'm concerned about the rewiring. I have a 66 coupe. It's been modded heavily I cant even find my hazards light switch.
 

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Sometimes the hazard switch is in the glove compartment. If you find the switch, turn it on. If it works you will hear a clicking sound. That sound will lead you to a flasher/ relay. The turn signal switch is under the steering wheel. You need to pull the steering wheel and unplug a connector at the base of the column and pull it from the top. Look at the picture. Lots of possible problems with these.
 

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Since your car is not stock its not possible for me to tell exactly what is going on. In a stock system the brake and turn are on the same filament and share the same set of contacts in the turn signal switch, and since the signal is working that shouldn't be the issue. Are both stop lights out? I can't imagine they changed the turn signal switch to different hardware. The schematic below shows how a 69 works- yours will be similar. Since this is a schematic it doesn't show wire colors, plugs and other things shown on a wire diagram. A schematic is intended to show how it works.
 

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If you can't follow the schematic above, here the stop circuit is highlighted. In a stock car, power starts at the battery + terminal, goes through the 15A circuit breaker inside the light switch, through the stop switch, through the LR and RR contacts in the turn switch, then to the respective light bulb filaments and finally to ground.
 

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Discussion Starter #19
Thanks everyone. Yes, my right brake light works but the left brake doesnt. Both right and left rear turn signals work
 

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On my 70 Cougar, I had a similar problem. There are actually 2 contacts in the turn signal switch for each side. One is the "lane change" contact and the other is when the switch is pushed all the way. The signal would not work when pushed all the way, the way the switch is mostly used. But when pushing it lightly, like changing lanes, it would work. Another time the brake lights were not working and banging on the steering column when pushing the brake pedal would make the brake lights flash. Just some possible scenarios...
 
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