Need help with 99 blazer with 4 button 4wd switch. My problem seems to be a little different than others I see posted. When vehicle is running the service 4wd light flashes on and all the lights on 4wd switch blink and relay clicks just like when you first start vehicle. It does this intermittently. I replaced the switch same problem. How do I know if it's the module or the unit on transfer case?