how do you get the dash apart to replace the headlight switch on a 1985 pontiac trans am?

Look online at www.Chiltons.com or just search, "1985 Pontiac headlight switch replacement" and see if someone has posted a video. I think what you will find is that there are two tabs (one top and one bottom) that need to be pushed (in or out) in order to release the switch from the back of the dashboard. You will have to remove the lower dash board cover below the steering wheel and "look up" behind the dash or feel around with your fingers to find it. When doing this type of work, I find it helpful to use a small mirror when trying to look up behind the dash, so I don't have to twist around so much. ALSO I would recommend disconnecting the battery just in case until the job is completed. Its up to you.

The hard part is disassembling the dash pieces to expose the switch. Start with the lowest panel (driver's knee panel at bottom left of dash) and work your way up until you can remove the switch. I don't recall if it is a push-in mount as Fordtudo37 said or if it is held in with mounting screws. Either way, once you get the dash peices apart it will be obvious - and easy.