Step-by-Step '67 Rallye Gauge Cluster Overhaul/Audio System Upgrade

I think that the LED bulbs do not dim because they do not pull enough current compared to the old bulbs. If you leave at least one regular bulb in they will dim. I kept incandescent bulbs in my aftermarket gauges for this reason. A bulb in your radio, or ac controls ( if you have an ac car) will do it too.