...headlight switch needs to be replaced .i just did this last month because my headlights went out like you (every thing worked just not the low beams .
1, you will need to remove the radio and the ash tray
2,pulling off the dash trim ...
a) pull it off half way ( carefull the pins that hold it into the dash are old and break easy
b) put the shifter into drive ( this gives you more space to work as your pulling out the dash bezel..... once you did that ,dis-connect the buttons for rear wiper/defrost/fog ( these can be a pita carefull not to break tabs that are on the harness's of the buttons .
c) after getting the buttons loose carefull fully wiggle the dash trim up and out of the way
3, the switch is held in there with either 2 bolts or screws ( remove them )
4, wiggle the hd switch out of the dash , once you have it out be carefull not to break the tabs that hold the wire harness onto the unit ( this is a must because the hd switch heats up so often and so much that everything thats connected to the switch is BRITTLE especiality one wire that is in the center of the harness ( must be main wire lead for the headlights)
5, once you got the harness undone you will see a spring loaded button under it .....pull the knob out all the way ( like if you were turning on the headlights ) and at the same time press in that spring loaded button .
may take one or more times of presssing and pulling on the knob before the knob / shaft slides out of the headlight switch .
6, unscrew the nut behind the knob and remove black metal backer plate ( the one you see from inside the truck / dash) take the plate off and save the nut and the knob ( you will need them cause a new switch will not have them )
7, go buy your self a new unit ( $20 at auto zone) they will ask you if your truck has power mirrors or not ( 2 types of headlight switches sold ) ,also since you got it out at this point take it with you to make sure they give you the correct part
8 re-install the new switch and when it comes to the backer plate ....it has slots in it so it only installs one way when slideing it back into the dash ( i did mine wrong the first time and could not figure out what was doing wrong )
i guess above all on what to watch out for would be the plastics on the truck
.....they are old and the plastics either being your dash trim or the wire harness's will BREAK VERY VERY EASY if you don't pay special attention .
goodluck
