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Here is the question - late 60's RR, GTX, barracuda all had single bulb dual element tail lights for stop turn and tail. In the era of no solid state trailer controllers how did the factory make that work???

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Wiring.
A constant hot wire went to the brake switch. (RE in the example)
This signal (Off/On) was directed up through the turn signal switch. (WH in the example)
No turn signal? it went straight through, feeding only the rear lights.
Turn signal? This completed a circuit ON THE TURN SIGNAL SIDE to route the ign on TS power thru the flasher (RE again here) to the front and rear bulbs. The other side was still connected straight through.