wing tip nav lights

[tx_swordguy]

I have the incandescent bulb type nav lights in the tips of the wings (end of the wing not a corner type light). I have not been able to get them to work since buying the plane in april. The rear marker light and nav lights are on the same switch and the marker light works but the tip lights do not. I am only getting 11-11.2 volts at the light socket on both wing tips. I am assuming that I have a bad wire somewhere but I cannot get the base plate off the wing tip. There are 3 screws that are very difficult to turn and act as though they are galling in the threads. Is there something I am missing in taking this base plate off? Bulbs are fine and work on a full 12v off a battery. I am guessing I am getting a voltage drop due to bad wire or light assembly but I cannot check the assembly if I cannot get it out. I was going to run a wire to the neg side of the battery and see if I get full 12 volts with no drop at the socket. I am at a loss as to how to replace any bad wire if I cannot get to the wing tip end of the wire. my only inspection hole is about 3' from the wing tip.
Mark

[mike.smith]

You'll probably need to link to some photos for someone to identify the product, and to help.

[EdW]

Sounds like bad ground, the most common cause of stuff like you describe. Loose connection, corroded socket/bulb base, almost aanything can cause this. Best advice? Learn some new swear words and plan on spending the weekend checking every wire and connection.

Ed