[Steve Vague]

Any electrical geniuses in the group? OK so maybe it won't take a geniuses, but I am stumped. I have switched my original two bulb tailights, to single bulb double filaments. Problem is brake lights and signal wires are now connected with pradictable results. When either brakes or signals are lit, all are hot. I should mention that this is on an Aurora, with four way flashers.
Should I be using a relay, (if so is there one recommended?) or diodes? Am I making this more difficult than it should be? Grounds are all secure as far as I can determine.
Regards,
Steve