instruments prior to VL weren't back lit, so they will never be as good as post VL onward model
The markings on the instruments when new were reflective, so when the instrument lights were on, they reflected the light and worked reasonably well
20-30 years later the effectiveness of the reflective markings are all but non-existent, so the effectiveness of the dash lights is greatly reduced.
I had the same problem with the VH. I replaced the main wiring harness connecter, by passed the dimmer switch and checked the voltage at the dash lights and it was getting full battery power, but still they were dull. I replaced all the light bulbs, still not much better.
So I replaced all the light bulbs with the T5 wedge LED's on this site
12v LED Dashboard and Instrument bulbs. They have 3 surface mounted LED's and are actually very effective in brightening up the instruments with a much brighter white light instead of a dull yellow light. The dash lights are quite good now, still doesn't compare to modern back lit instruments, but you will never achieve that unless you somehow managed to get the instrument facias re-manufactured to suit back lighting.
The VK I believe uses the larger T10 lights, which the website above also stocks
