I have a 64 valiant convertible. Both left and right Rear turn signals work but only left brake light works. Anyone know what I should look at first to rectify?

Right brake light bulb would be where I would start.

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Casually looking for a Clifford hyperpak intake for cheap.

The same filament in the same bulb is used for the brake light and rear turn signal functions; the OP says the left and right rear turn signals both work, so it's not a faulty bulb. It's a faulty turn signal switch. The power for the brake lights goes through the turn signal switch; that's how those bulbs do double-duty as brake/turn signal. When the switches wear out, one of the first symptoms is loss of one brake light. Install a good quality new turn signal switch and the problem will go away.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

And then I would wait for Dan to correct my too-quick-to-judgment and incorrect diagnosis. I am getting over a nasty flu bug or I would have remembered that the filament for the brakes and turn signal is the same. I will go back to lurking mode until my head is completely clear.

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Casually looking for a Clifford hyperpak intake for cheap.

Thanks for the advice. I assumed it may be something related to a dual function switch. I will try to find a new switch. One more question. What if you are born on second base ?

That work has already been done for you -- just click the red "new turn signal switch" text in my post above, and you'll be taken to the right page to source a good new switch.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Same assumption except a life time of whining being robed of a triple.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC