1991 GMC Sonoma Q&A
1991 GMC Sonoma Question: Dash lights and interior light went out.
I would check the headlight switch and dimmer switch. It's best to have a wiring diagram to test these so you know which wires to check. You can get a good wiring diagram here: http://bit.ly/mitchell_repair_manuals_online You can use a test light but a voltmeter is preferable. Check the power wires that go from the headlight switch to the interior lights. Good Luck! - Bret Bodas
As far as interior lights,my '91 Sonoma has rubber grommets around the door switches that have deteriated,letting sand,dust,etc. get into switch.Just spray some lubricant in there & push in/out & see if dome light works. - Visitor