This is good one for all you 123 owners. For all of us that have driven these great cars there are some "blind spots", literally. One of these "blind spots" is in the dash lights. I think all of us familiar with these cars must admit that the actual dash running lights on the 123 chassis vehicles are lacking. The reason for this lack of intensity is the way the lights work. There are two bulbs that send the light up through two separate light tunnels and then it is reflected back onto the face of the instruments. Some of the light intensity is lost in this transfer.
If you remove your instrument cluster (if you are not familiar with this operation please see our "Instrument Cluster Removal and Component Replacement Guide") you will notice the light tunnels along the top of the cluster housing. With the cluster removed and the wiring still attached, you can turn your dash lights on and actually see light leaking through the cracks in these light tunnels. We discovered it is worth sealing these leaks by using aluminum tape as shown in this picture. The aluminum tape can take the extra heat from the lights themselves and will not deteriorate as other tape would. Two short pieces as shown are adequate.
Note: Do not expect a huge increase in light intensity. This modification will give a small improvement and depending upon how bad your cluster assembly is, you may or may not see a marked improvement in your dash lights. If your lights are still super dim you may have a bad dash light dimmer switch (poteniometer). Corrosion on the rheostat can prevent full voltage from getting to the light bulbs. I sometimes just remove the switch and throw it away. It's okay since I have never personally needed to dim my 123 lights. If anything I always seem to want to crank them up.
So if you are having problems with your potentiometer switch, you can remove it and put a jumper wire between the two posts on the back of the instrument cluster that the potentiometer plugs into. If you install a jumper wire between these two posts it will give you full 12 volts to your dash lights. For all of us who love these 123 chassis cars it's nice to have bright dash lights.
