Here is a wiring diagram for the 87 turn signal circuit:
The notchback (aka SE) routed the power for the brake lights through the turn signal whereas the GT ran a separate wire to the back just for brake lights. Looking at the diagram, there is a white wire that comes from the brake pedal switch and goes through the turn signal switch. This is how they get one brake light to flash while the other one stays on when you put your turn signal "ON". Now for some reason the white wire runs from the brake switch, all the way to C500 pin H8, and then back to the turn signal switch. Remove this wire from pin "H8" at the C500 connector, this eliminates the routing of the brake lights through the T/S switch. You can now use that wire to run your brake lights separate from the turn signals. The turn signals will still work normally because they receive power from a different source ( the purple wire from the T/S flasher). Essentially, this is how they do it for the GT models except they used an extra wire spliced at the brake switch and running back to the C500 on pin "J9". I'm not sure you will find that wire in your harness if your car started life as a notchback. If you do have a light blue wire at pin "J9" on the socket half, you could add a pin to the the other half and use that to run brakes lights as well. You would need to eliminate the white wire from "H8" though otherwise both turn signal and brake lights would flash. I'm not sure how your harness has been modded for the Lambo lights, but you will need to use different sockets and single filament (1156) bulbs for your new turn signals and dual filament (1157) bulbs/sockets for the tail/stop lights.
Finding a taillight harness from a GT would simplify things because it already has separate turn and stoplight wiring.
[This message has been edited by seajai (edited 04-04-2014).]
