I don't know about the bonneville, but the thrux has 2 lights in each instrument. On mine not to long ago, the bottom light went out. It's no sweat to replace, just take off the back cover of the instrument, be careful because they have shims in the stud that the nut is on, then pull out the bottom light.
May I suggest replacing the lights in your cluster to LED's.... I did and made a world of difference. Also used green leds to match my bike color. silly I know, but looks cool. I bought red ones to in case I want a change down the road and am doing a lot of night riding.
superbrightleds.com is where I found them. There may be others that are cheaper, not sure.
Just be carefull if you decide to change out the warning lights, when I was replacing my neutral bulb with an led, I somehow fried (or suspect I fried my neutral switch) located under the bike. It all might have been coincidence, the fuse was blown as well. I just assumed the pop I heard was that switch. Might just have been the fuse and the switch was on its way out anyway.
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