I have a 2004 Ford Taurus. The left break light does not work but the left turn signal does. The right break & turn signal both work. The turn signal & break light are in one bulb. Moving back from that bulb there is short wire trunk the plugs into a much longer wire harness. I have switched the left & right short wire trunk and the problem remains on the left. So, I know it is not the bulb or that short wire trunk. I really don't understand how this is possible.

Thanks for you help in advance.

Sounds like maybe the Signalhead(Combination Switch)Turnsignal Switch. It has different names. Good Luck

See if this video can help

https://www.youtube.com/watch?v=n8nxDefhI4M

How do you know its not the bulb? Have you replaced it, they are usually dual filament bulbs on almost all cars (in fact ALL vehicles I have ever owned over 40 years). One filament handles turn signal/running lights, the other brake light. One filament usually burns out before the other.

When troubleshooting signals, I like to put on the 4 ways and walk around. If all the bulbs work. Bulbs and wiring are good. Hazzards are Fused Constant Voltage, and most? Turn Signals are Ignition Switched. If a bulb was out in the old days, that side would not flash, with modern Electronic Flashers, the Bulbs Flash fast.

Could only be the Combination Switch.

Sorry for the delay in my response. I just forgot I posted this. So "Signalhead(Combination Switch)Turnsignal Switch" where is it, how can I find it?

I'll replace it but I need to know where it is.

Thanks

I found a video for replacing the multifunction switch. Apparentlythis is a known issue with these models. I have already ordered a replacementpart online at CarParts.com. After I replace the part I’ll post an update.Thanks for your help.

https://www.bing.com/videos/search?q=turn+sigle+switch+for+2004+ford+tauris&view=detail&mid=B922154C0661C35BA8C6B922154C0661C35BA8C6&FORM=VIRE (https://www.bing.com/videos/search?q=turn+sigle+switch+for+2004+ford+tauris&view=detail&mid=B922154C0661C35BA8C6B922154C0661C35BA8C6&FORM=VIRE)

How are you doing with this? Thanks
Videos sure are nice. Good Luck

All is well that ends well. Because the problem was the break light I would never have thought the source was the Multifunction Switch. In fact I didn’t even know what a Multifunction Switch was. Thank you Stratmando,you were right on. The most difficulty I had was getting the ignition switch out. I just could not find that little bump that releases the switch. It took along time for me to find it and it was really frustrating but eventually I got a hex key on the right spot and out the switch came. The good news is that all the various functions the Multifunction Switch controls work and so do both breaklights. Thank you everyone for your contributions

Thanks, Here's why it had to be the Switch. Stop and Turn use the same filament, since one worked and the other didn't, that said the wire to multifunction switch was intact. And with the other side working for both, that said fuses were good.
Thanks for toughing it out. Good Job.