My 1992 f150 4x4 has very dim head lights

Yes

http://9.dfbm.dominik-suess.de/htr/1992-grand-marquis-engine-diagram.html

You should be able to get a diagram here.

Sounds like the alternator output is low. Not enough output to charge the battery. Your local advance auto store can check this for free to be sure. It could be the battery not holding a charge like it should. Check it first with Adavance

there might be two options the altenator is going out or blwer motor is locked or burn"t out afther derk start car and turn lights on in front of garage door rev the engine up if the lights get brighter the charger is working and maybe blower motor is going out

Look for the relay for the head lights,it may be bad.Also look for a bad ground.And check the bulbs too.

If voltage regulator is good, then the dimmer switch is probably bad.

If you're running the car under a heavy load, lights will dim briefly (ie. you turn the ac on full)

With the engine running, the leads on the battery should read 13-14V

You Digital dash is working as it should, it is supposed to dim with the lights on so your eyes don't have to adjust, from looking ahead to checking speed and back

These problems are always frustrating. Some of the charades swicth directly via the stalk on the column, while others have interposing relays. A common problem with dimmed headlights, indicators and dash lamps on the charade is caused by the fuse box retaining screws becoming loose .... these screws are also the -ve path back to the battery via the chassis.

If you have a meter, check voltages between the fuses and various metal parts to see if you can suss out a poor continuity path. Check your chassis strap between the battery -ve and the body is clean and tight.

it the voltage regulator in the alternator turning on and off...when it turns on the lights will get a little briter....when it turns off lights will get dimmer

You must check all of your fuses. It's most likely one of those. Dash lights are also controlled by the intensity knob on either your headlight switch or possible near it. It will dim/brighten your radio lights and interior lights too.