From jktowers1@googlemail.com@21:1/5 to All on Fri Feb 5 00:24:58 2016
I get this on a lot of head units, even those with dimmer wires. I take them apart (carefully) then put a small amount of black paint over each bulb, covering about 50% of the bulb in each case. I find this works for me.
I believe they are set so bright initially so that they look good in shop displays.