Pulling a new wire can be done, but it can be tricky. First, you have to figure out which wire is bad - not easy in itself - and then cut it off at both ends. Then you have to maneuver a new wire through the rough-cut channel in the foam inside the ceiling, as the end of it snags on the foam as it moves. This can be really difficult if there is a bend in the channel - and there is always a bend in the channel. Here is a different - perhaps less desperate - approach.
Get yourself a fistful of fuses - they are cheap. Now dismount (unscrew) the fixtures, one at a time. After removing each fixture, check to see if the fuse blows or stays good. This should tell you which fixture is causing the problem. Once you have identified that, you can continue in one of two directions.
My guess - and it is only that - is that the problem is not caused by a screw piercing a wire. The problem may be in the fixture itself. The fixtures are constructed with a lot of bendy metal pieces and a lot of sharp metal edges. In addition, the hole cut in the bendy aluminum skin of the TM ceiling is also sharp, and as you push a wire back into the hole, and screw the fixture down tightly, it is easy to pinch the wire against a sharp metal edge, cutting through the insulation. So examine the fixture carefully for something that doesn't look right. Examine the wires that go through the hole in the skin, looking for a cut or abraded spot. By the way, there is nothing wrong with cutting the hole in the skin a bit bigger, to give a little more room for the wires that go through it.
If I am wrong about the fault being in or near the fixture, then remount the bad fixture, one screw at a time. This may tell you which screw is causing the problem. If you can identify the offending screw, then dismount the fixture and figure out which wire heads toward that screw after it goes into the hole in the skin. If this tell you the story, then you can probably insert the end of that wire into a length of soft plastic tube and push the tube down the wire until it reaches and passes the location of the screw. This gives you new insulation over the faulty location in the wire. Push the newly-insulated wire back into the hole, being careful not to pinch it, and push it a bit to one side of its previous path, to get it away from the offending screw. Mount the fixture, and check again proper operation.
For "soft plastic tube", I am envisioning what is called heat shrink tubing, available in the electrical section of hardware stores. It is flexible, reasonably tough, and comes in a lot of sizes. Pick a size that lets you slide it down the wire easily - but of course don't shrink it - just leave it loose.
Although what I have outlined is annoying and time-consuming, it may be a lot better than trying to run a new wire through the cramped spaces inside the ceiling.
Bill
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