Changing gauge cluster light bulbs - How To

French demon said

I think that you should make a "bench" test, out of the car and bypassing the dimmer, with a battery or a battery charger.
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This way, you'll get the max power the bulbs can give.
If you get the same illumination than me with my '68 Valiant cluster, you'll be sure that your problem comes from a bad grounding or a defficient dimmer.

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Late to the party. I'll point out that only 1 of two illumination circuits is identified. The smaller board also has the orange wire feeding 2 of the 4 bulbs.
I do have an aftermarket stereo head unit in my rally panel along with it tiny LEDS. My instrument panel retains the incandescent bulbs with blue tint diffusers to maintain that OEM coke bottle green tint appearance that is always had. I did bypass the dimmer feature on the headlight switch, so they are as bright as they could be, failing dimmer or not. Just personal preference, different stokes.