They make in-line led dimmers for like $3, so rather than wiring in resistors, I'd just put in a dimmer for infinite adjustments and could easily adjust again should I swap out a gauge.
The brightness variance is due to different eras of gauge technologies. The original ones from Barb have a thick cardboard face the don't allow for any backlight penetration, only side lighting...where as the (assuming newer) ones do, so those appear brighter.
It's all good...I'm looking forward to a fuel gauge finally!
Sent from my M9300 using Tapatalk 2