Well, your gonna need a new ring. AFAIK, thats going to be a junk yard item, or you buy an entire new switch.
To get the ring on/off you need to get the knob/shaft out of the switch.
To do that you need to pull the front of the dash off (just the part facing you).. its only a couple of screws by the ashtray (pull the ashtray out).. After that you can just pull the front panel off the dash as its just clips.. If you have electric 4x4 you'll have a plug to pull off the back of the 4x4 switch to remove too once you get the panel pulled away some..
Now that the front panel of the dash is off....There are a few screws holding the headlight switch into the dash (the mounting bracket).. Take those out so you can get to the back of the switch..
Now look carefully and you will see a button on the top of the switch. I'm pretty sure its on the top and the wires are on the bottom but I may have it backwards. Push in the button and pull the switch knob/shaft right out. You have to find the sweet spot. Push the button too hard and the knob won't come out and the same happens if you don't push it enough..
Note: I highly recommend that you disconnect the battery before working on this so you don't short anything out (like when you disconnect the lighter as you take out the ashtray) or end up with the headlight switch in the on position as you plug it in etc..
~Mark
