There is no ground wire associated with the headlights. The mountings provide the ground. There should be two or three wires leading to each headlight, depending on whether you have cowl lamps or not. You could disconnect the plugs on the lower rear of the headlights (they are bayonet fittings) and check for voltage there. If none there, you could check at the dimmer switch and then back to the light switch. A number of possibilities in decreasing order of likelihood, but all things to check:
-- Burned out bulbs (maybe caused by using a12V charger or jump start and having the headlights on)
-- Corroded or damaged headlight switch contacts
-- Corroded or damaged dimmer switch
-- Corroded or loose connections at the headlights
-- Poor ground at the headlight mountings (you can easily check by holding one end of a length of wire on the headlight bucket and the other end onto the negative terminal of the battery. If the lights come on when you do that, you've found your problem. Just unmount the headlights, clean up the mountings and you're done.)
The disconnected wire could well be a disused horn wire.... Just a guess.
You need a wiring diagram for your car to help troubleshoot this. There is one in the Repair Manual for your car which is available from filling station.com. I also have one in electronic form that I could send you if you'll send me a PM with your email address.
Hope that helps.
All the Best, Chip
