Finally got the darn plastic pins loose from the fresh air and heater levers so I can access the rear of the panel to troubleshoot the dim bulbs on instrument panel.
There are three bulbs: two inside sealed speedometer unit. This unit has the speedometer and to the left of it, the gas gauge/turn indicators/GEN and OIL lamps. One other bulb is in aftermarket VDO tach mounted to the right of the speedometer.
The two bulbs in the sealed speedometer/gas gauge light very dimly. Hard to see at night.
The GEN and OIL lamps light normally. The tachometer bulb also lights nice and bright.
The bulbs in the speedo/gas gauge unit and the nice bright one in the tach all come off the same dimmer knob, so the dimmer rheostat is fine.
With engine off and lamps on, voltage measured from wire at rear of speedo/gas gauge lamp holder to chassis is 11.6 volts. Same measured from lamp wire to ground terminal on rear of sealed speedo/gas gauge. This suggests that the ground connection from the sealed speedo/gas unit is good. And that there seems to be sufficient voltage present at the lamp holder to light the bulbs okay. But they are quite dim.
I have to think that either both lamp holders are housing very dim bulbs, or the connection - on both holders -- to/from the bulbs is poor. Wiggling the lamp holders makes no change.
I'd like to pull the holders out to examine them. Bentleys and Muir are silent on this matter. Type2.com's library does not seem to cover this detail.
They appear to be black plastic assemblies pushed into holes on the rear side of the sealed speedo/gas gauge unit. Do I just pull on them?