running/brake light issue

I have been searching the forums for some clues to this issue with no luck ... I installed a new brake light on my '78 KZ 200 and cannot figure out why all of a sudden the brake light is on all the time - no running light ... first check was the rear brake switch - not it ... I even disconnected it so it is definitely not too tight. Next check was the front brake sensor ... not it either that I can tell.
I can disconnect the rear brake wires entirely with and the light stays on; and I can disconnect the front brake wires and it stays on. If I disconnect both, it shuts off, and obviously, if I disconnect the light it goes off.
It seems like for whatever reason the wiring only wants to light the 23W filament and not the 8W filament on the bulb.
Anyone have any ideas of what it might be, or something else to check?

most likely you didnt get a good ground when you put in new tail light. tail light is grounding thruogh the brake light circuit and light it as well.

I'll try the ground ... this new unit is grounded through the mounting bolts though, not a separate wire ... I had left the ground from the wiring harness grounded to the fender mounting bolt, but I will try it directly to the new tail light.
Thanks.