[torbjorn]

Probably the simplest way is to disassemble the radio's front panel, determine why the no. 1 button isn't working and then repair it. In most cases, there are small "TACT" switches behind each button. Those do often fail and similar switches can often be re-used from other scrapped pieces of electronics (VCRs, computer mice, clock radios and so on).
If the radio has a rubber membrane keyboard (like those found in tv remote controls), then it is common that the plasticizer agent has sweated out of the rubber during the years and fallen out on the PCB. In this case, wash the rubber membrane thoroughly (hot water, detergent and toothbrush, then flush with plenty of clean water and set it aside for drying. Don't touch the black conductive rubber pads after cleaning. The PCB should also be cleaned. If it can be easily removed from the radio, then the same treatment with detergent and hot water is suitable, in other case it is better to use methylated spirits and cotton swabs for cleaning the contact surfaces.

[bugleflugel40]

I have a RDS 500 Ford car radio. I cannot enter the 4 digit code owing to Number 1 button not working. Any ideas?? Needs a 4 digit code using buttons 1-4 - I know the code but I cannot enter it!! Very grateful for any replies :