..... how funny I have the same issue.... When I bought the car...everything was working. Also the Cluster lights...
last week I had to remove the Steering Collum... guess what happend ? The Cluster lamps were out of order.......
I checked all wires.. nothing..the I made a Jumper wire from the light Switch ( black cable ) to the dimmer Switch...( also black cable )
the lights worked !!
But the Story goes on.... had to remove the Steering Collum once again.... because of changing the steering gear box...
and the lights were oof again...
I am really confused now..... because I didin´t touch the "Jumper wire...nor the dimmer or light Switch....
The only thing I found out...that the fuse on the right top of the fusebox is allways "cold" no power at all....
No telling how this applies to you, if at all... But when I got my 72 Cuda I had all kinds of electrical problems... dimming headlights, alternator not getting power so not charging battery.. VERY low power coming into the dash gauges etc. People kept telling me it was the voltage regulator, or the alternator... No! The main, (And easiest), fix was the fusible link in the engine compartment near the battery... it was black and partially burned under all the tape. Once that wasn't messing up all the car's electric power it was much easier to get the rest figured out. Just in case you didn't already look?
i found some "burned " wires... not badly.. but I renewed them...charging system works....14.7 Volts at the battery.
So far so good.. The only problem I have is always the same ....Cluster lights don´t know why... Tomorrow in the afternoon I will continue my "search. As soon as I get some results , I will Keep you informed
The lights are working now !! What was wrong ? A simple "cablethief" wasn´t set poperly....it didn´t make a good contact to the second wire ...so the Dimmer Switch had no "Input "...
Used a new "cablethief"... result Clusterlamps are workin now