its the alarm telling you your lights are on this happens when you open your door so your door may not be closeing right
the chime would stay on if the keys are in the ignition (but the car turned off) and if the door is ajar to warn that the lights are still on
Bad ground on the brake lite circuit.
Alternator
that chime is telling you that the door is open if you have owner manuel, you can find in manuel how to turn off the door open chime from working
I know I already answered this question, but I will answer it again.. The chime that does the headlights also does it for the Key in the Ignition reminder. Sometimes these small switchs can go bad, and key cylinder lubrication can sometimes fix the problem, but more often than not, the key cyliner has to be replaced. The cheaper route is to just remove the chime box, by following the sound until you find it and unplugging it. However, this will also mean if you leave your headlights on, you wont know...
Possible ground issue at the taillights.
i would consult your maunal and look for your "lights" fuse and that should turn them off once its pulled. im not quite sure what it would be labeled but it sould say "lights" or "Alt Lights"
Check the fuses.
I would replace the headlight switch as Ford has had their share of these problems.
Headlights run off the battery not the ignition...
A bad ground wire will cause dim headlights, or will cause lights not to work.
try turning your dimmer switch Also check your wiring, in my 89 LX it has the digital dash and that was the problem