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Wouldn't it be simpler to ground each signal to its own stalk, which is bolted to the frame, or am I missing something?
JSK,
Are you missing something? Well, maybe Yes and maybe No.
In this discussion will need to make distintion between when talking about the entire t/signal assembley, and when talking about just the t/signal bulb socket itself.
Okay, lets proceed. This discussion may get a bit detailed, but I think I am up for it.
Here is a picture of GS rear t/signals that I have had (80 GS850G).
THis shows two rear t/signals, each still mounted on that bracket.
Hum, picture does not really show what we need to talk about.
Can only somewhat see the one wire (black) that comes out from the turnsignal stalk and the other wire (ground wire) (blk/wht) that is from the ring terminal on the stalk. And cant see the mounting nut.
Here lets use this (78 GS1000), shows one front t/signal and one rear t/signal:
Can see that the t/signal itself has only one wire comming out through the stalk. That wire runs thru the center of a metalic treaded pipe. So, if you think of the light bulb itself and the socket that the bulb plugs into, that socket must be "grounded" thru that metalic threaded pipe that runs through the plastic assembly. And, yes, if that treaded metalic pipe is grounded, then, yes the light should work when power is on that one wire.
But... but .... BUT, if mounted in it's stock manner, that threaded metaic pipe is NOT grounded thru the way it is mounted. Notice that the entire t/signal assembly is mounted in the rubber grommett (#7). I suppose the rubber grommet is to provide some isolation from the mechanical vibration, but then it also makes for electrical isolation, hence the need for the ground wire / ring terminal (#11) to ground the threaded metalic tube.
So, if the t/signal stalk is mounted in that rubber grommett, then it will need that ground wire added to the stalk.
If the t/signal is custom mounted directly to something that is electrcally connected to the frame and frame is well grounded, then will not need that ground wire. But I would recommend the ground wire anyway just so not relying on that nut or whatever to keep a good ground contact.
So, what you maybe "missing" is either not having that rubber grommet or not noticing the rubber grommet.
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After understanding all that, let me make An additional comment relative to improving the wiring of the turn signals:
Look at that black wire right at were it comes out of that metalic threaded tube. If it has been bent over at that point, the insulation may be cracked or maybe otherwize thinner than it should be. This is a potential failure point were the insulation can fail and then the wire shorts to ground and is hard to find what is blowing the fuse. (when I had this problem it was intermittent, would only happen once every couple weeks or so, was annoying...)
What I recommend is this: Take off the lens, and find the screw (not shown) that mounts the bulb socket (not shown). Remove that screw and pull out the socket just-only far enough so that damaged portion of the wire is exposed (but not far enough that pull entire wire thru the tube). Put a couple turns of black tape over that area to reinforce that part of the insulation, just a couple turns of tape (if more then cant get it back in. Then pull the wire and socket back into place, and reassemble. << Later note: this description of how to reapair/improve this wire is from my memory, which is suspect. But anyway, the general idea is to take it apart so can get at the wire right where it comes out that tube and add a couple turns of black tape. Better yet, take it completley apart and use some heat shrink tubing, but will then be harder to put back together.>>
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