Gr8uncleal wrote:  "I've repaired quite a lot of these old switches and test the circuitry by attaching my test lamp, via a battery, to the brown/white wire terminal and each of the dark brown and dark green in turn. When working correctly, each side only lights up when the switch is in that position."

Yes, what you said is true IF you are testing just the switch.  It would not be true with the switch connected to the wiring harness and probing the wires where the signals connect on the bike.

I went back and read my original answer in this thread and changed the wording around as it wasn't as clear as it could have been.  *I* knew what I meant though!

I've had this same puzzling thing happen to me many years ago and spent a long time chasing my tail trying to figure it out...  which I finally did.  It's simply the way the indicator light in the gauge is wired so that the little bulb grounds through the the filaments of the opposite side signal lights.  Genius wiring but confusing as heck when probing the harness with a test light

Yes Mark, testing my repaired switches only, on the kitchen table! 

Mark is the winner ding ding ding ding! I was thinking about this last night and thought about the gauge indicator bulb being for left and right signals. I removed that and the power went where it was supposed to go. I now have 4 working signals on this bike!

I knew it had to be something simple because there was no hacked up wiring on the bike.

I am also using all incandescent bulbs.