Go to O'Reilly's or AutoZone and get a standard auto relay. $5 or so. They also sell them at Radio Shack. Here is the wiring. The 4 wires going back to tail lights are:
brown - ground
blue - work light positive
orange and red/yellow for tail and brake.
The relay has numbers on the bottom side and here is how to wire it:
relay 85 and 30 tied together to red/yellow
relay 87
relay 87a to red
relay 86 to orange
relay 85 to brown for ground
This will make the tail lights come on with the key on and/or headlights. Then the brake pedal will activate the new brake lights
Here is a link that explains the relays and has pictures and wiring diagrams.
Basic Wiring - Custom Airbrush Work and Radical Customizing