Re: Adding a 3rd Brake Light to a '67
Rick, it looks like the one you posted a pic of is their AT-LC-1 logic and it's been replaced with the AT-LC-4, which has a additional terminal for a ground.
If they're description is accurate, if you have a turn signal on then step on the brakes, it will sense both then latch the third light output to on. It'll latch and hold on the output until BOTH light inputs are off.
In other words, once latched, it'll maintain the third light output even though one input is flashing.
I'm not sure how or what the circuitry is but it's worth a try.
The only slight issue is that if a flashing turn signal is on when you let go of the brake pedal, the third brake light may stay on until the flashing light is off between flashes. This could delay the third brake light from going out for a second or so. This wouldn't bother me.
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1971 Monte Carlo SS454-496ci 600hp
1999 Trans Am-500hp
2003 Iszu Ascender XL Limited V8