Heater control head lighting, works..then not.

[MAC71Cheyenne]

This one has me stumped. The bulb n socket on the right side work fine when it is out of the head and grounded by just touching the bottom lip of the dash or the back of the head. Once the bulb/socket is fully inserted it goes out. Socket tabs are making contact with the case its not loose, and bulb is fully seated. As soon as you loosen the socket and back it out a smidge it lights up. No strain on the socket wire...

The wire and socket for the left side blower speed is m.I.a at this point but moving from right to left it lights up but is dim. There is no other wires touching the controls with the exception of the blower switch wiring.
Sounds like a bad ground or short but test light grounded to the head lights up like it should and is not dim.