Temperature gauge

[Mario]

My temperature gauge starts to go up when I turn on the parking lights or headlights.  I also don't have the gauge lights working.  My truck has been parked a couple of times, so I can't remember how things happened when they happened.  What would make the gauge lights affect the temperature gauge?  How do I isolate the gauge lights from the temperature signal?  Thank you!  Ohh...  It's on my '81 K20.

[bd]

• Make sure the headlamp switch knob is rotated all the way CCW just short of the interior light detent. 
  
  
• Check the instrument lamps fuse.  Make sure it isn't blown and that the fuse contacts and its fuse box socket are completely clean and free of oxidation. 
  
  
• Check the instrument cluster bulbs and make sure the bulb sockets are making good connections with the printed circuit board (PCB). 
  
  
• Verify that the instrument cluster harness connections to the PCB are clean and free of oxidation (shiny).  Use a soft pencil eraser to polish the connections if needed, but be careful that you don't peel the fragile foil away from its plastic backing. 
  
  
• Check and clean the cab interior ground connections to the ground bus bar located on or near the parking brake pedal assembly on the left kick panel. 
  
  
• Verify that the ground strap between the engine compartment firewall and the back of the right cylinder head is installed and snugly attached to shiny clean metal.