[Healeys] Third brake light

[Fred Wescoe]

Lister's,

I have installed a third brake light and I need some insight.  I have tried
what I think are all of the wiring combinations at the driver's side, rear
tail light.

I can get the light to work properly with the brakes but then it will also
blink with the left turn signal.  If I then change the wiring, the third
light will work with the running lights but not the brake lights.  And so
it goes with each different combination I have tried.

Can anyone with a properly working third brake light clue me in on how to
wire this?

Thanks as always,

Fred
63 BJ7