Well, generally the 4 light "visual check panel" as it is called usually has only one working light for the std. cougar unless it was ordered with some options.
The one usually working is the first one on the left. Your parking brake light that is red and flashes when on. the other lights are for door ajar, low fuel, ( both red ) and the last one is blocked off in nearly all. Most std. Cougars did not come with the low fuel or door ajar options although the slots are there and it was an option available. My std. convertible just has the first one, the parking brake on light and it works perfectly. Yours should to unless the switch on the parking brake foot lever is bad or the bulb is burned out. Both easy fixes. Hope this helps.