So I did some investigating on that relay diagram that you posted Bartamos. I couldn't get it to work as drawn, but with a small modification, it works like a charm. The flasher load wire shown in red on the diagram just needs to go to the turn signal switch and not to Pin 87 on the relays. The signal coming back from the turn signal labeled signal switch left and signal switch right makes the relays do the flashing, switching the appropriate brake light on and off. The attached is the modified relay diagram in case someone else is wanting to use a 4-wire turn signal switch without adding separate lights on the rear.
I believe the diagram has to stay the way it is and a power wire, not shown, goes to the turn signal switch. Are you positive you got it to work with nothing on 87? Brakes work? Brake shuts off and rear bulb then blinks with brake pedal pushed? You used a 4/5 wire vintage switch? On a dual filament bulb? I guess I should ask is your result by theory or empirical?
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
