1999 GMC Suburban Ignition Problem

I have a 1999 GMC Suburban that has a strange ignition problem. On very hot days or very cold days the ignition switch turns just fine but the starter does not engage. If I turn the switch several times back and forth it will sometimes engage and start. Is this a switch problem? My battery is fine so I know it is not that.

Welcome to AF, no quick answer here, when this occurs you must check for 12v to the wire at the starter solenoid ( usually purple) that recieves current from the ign relay or switch.If ok solenoid is bad if none this must be traced back thru the trans position switch, relay if applicable and ign switch.

Thanks for the tip. I checked it and indeed there was 12 volts. Replaced it and all is fine.