Sounds like it is the dimmer switch. I'm having problems with my 87 so that when I first turn on the lights the low beams don't illuminate. I have to put them onto high then back to low to get them to come on. Sometimes when driving at night with high beams, dimming the lights causes them to go out. I was dreading having to pay someone to tear the column apart and replace the switch.
Then I found out that the dimmer switch is actually bolted to the column, just above the pedals. You do have to drop the column away from the dash to get to the bolts that are on top of the column. Before ordering a new one, you might check the rod that runs from the multi-function lever to the switch. I don't know if it can be bent, but that might be the case. The switch can be operated by hand just by pushing the plunger where the rod fits into it, once you've dropped the column.
The ACDelco part number is D8041A. I just bought one from Rock Auto.