Run a lead from the housing to the black wire for your ground. You'll just have to see which lead is which from the light (but I'll bet even money that the red lead from the light will go to the blue lead in the harness).
One thing I learned from my Lucas look-alike install on my Bonnie, if you get the brake half of the lamp hooked up as the running light you may not be able to tell when the running light half comes on (when activated by the brake circuit) since the running light portion of the lamp is only half as bright. Thankfully the wires are easy to swap about and all ended well.
