GMC53,

Improper grounding can send voltage through places it shouldn't be as it tries to find a good connection to the battery. This can result in mysterious readings with a meter.

If you have the drivers side light working you are half done...hooray! If you still have your neighbors help, use the continuity function on the meter and verify that each socket in the questionable light has continuity to the metal housing. If this pans out, the metal housing must have a good ground to the bed/frame when it is mounted. Scratch a new patch on the little lead tit on each bulb base and do a little scratch to the tit inside the lampholder. This is a real simple deal and you're almost there.

Stuart