[vatdevil]

Installed a turn signal to brake light conversion module made by Signal Dynamics (Tri Star XP). It splices into the rear wiring harness in the trunk.

I now have the following rear light functions :
Top light: brake, turn, running
Bottom light: brake, running

This solves the useless bottom light issue. I also upgraded to a brighter incandescent bulb. Both turn and stop lights are clearly visible in full sun.