4 pin mini-XLR: what's the 4th pin?

[Clueless]

I wanted to connect some PCC-160 stage mics to some Shure wireless transmitters. I stupidly thought that the Shure's mini-XLR would be 3 pin, so I spec'd some cables that were mini-XLR M to mini-XLR F. Imagine my surprise when I disover that there's a fourth pin in the Shure. Leafing through some catalogs, it appears that other wireless transmitters are normal 3-pin mini-XLR. What's the deal with the Shure? Is there some simple cable/resistor network I can make to make my stage mics compatible with the Shures? Or do I need to switch to a more compatible wireless system?

[brianroth]

Which Shure transmitters are you using? I just looked at the Shure website and opened the first manual I saw, for the UHF "Access". It states the input is unbalanced, with connector pinouts:

1 = Ground
2 = +5 VDC (I presume for powering an electret)
3 = Audio
4 = "tied to 20K resistor and audio ground" (electret DC return?)

Bri