You will be changing the turn signal into turn & stop. I did it with relays, one for each side. The relay is used to select which circuit to feed into the brake filiment. The trigger is taken from the front running light, which is normally on, until the turn is selected that side. So when the trigger is powered (closed), you have the relay selecting the brake circuit to the bulb - and when it's open, the turn circuit is selected. This requires a 5-pin relay with normally-closed and normally-open pins (not two pins the same in a Y-harness). See my write-up and circuit at
http://www.horseapple.com/Valkyrie/Tech_Tips/VTX_signals/vtx_signals.html The circuit diagram shows the circuit just for the brake filiment. Of course, with 1157 bulbs, you would connect the running light circuit to the running light filiment - and not do the part on the left side, with the resistors, and omit the diodes. Here's the circuit again:
