The most common causes of the issue you describe include:
There probably may be some more causes that I can't think of now.
either a blown fuse or bad headlight switch
You more than likely need to replace the headlight switch. Lights not going out when turned off is a symptom of a bad headlight switch.
You have a broken wire.
I would go to the high beam switch next (test not replace)
Try replacing the turn signal assembly. Everything is built into it.
the headlights and the tail lights will not turn on when i press the switch, also the dash will not light up like it it suppost to. i checked everything except the wiring. what is the best place to find headlight specific wiring diagrams?
It really needs to be checked out but it probably is the headlight switch itself that is malfunctioning.
Is it possible one headlight has been burned out for a while, and the second one going made you notice it? If not, I would suggest the headlight switch as the next most likely part.
not sure if this is the answer but have you checked to see if you have a ground wire that is loose or the connection is bad? as a bad ground connection will give you less voltage to the headlight/headlights and they will be rather dim. check your connections to make sure they are snug.
In october 1999 a recall came out for the headlights on ford thunderbirds and mercury cougars that require a new headlight switch with an incorporated circuit breaker contact the local ford or mercury dealer and they can help you out
Have you checked to see if the brights are not just burnt out? Rarely do they both go at the same time, but it is possible.
It is possibly a switch problem. If you can get to the switch, put a jumper wire to the two contact points (hot side and ground) with the key on the lights should come on and then you know the problem is the switch. psg