key code ?

In my 1991 Yreg Citreon Relay van there is a small key on dash with code underneath it ,comes on and ive to sit for at least half an hr turning the key on and off until this (yellow ) key goes out then my van starts ,ive sat impatiently doing this for the last few wks now someone said it is the key not registering but i don't know and would like a second opinion before i put it into a garage .