1981 K5 Blazer - Oil Pressure switch wiring

[mark97213]

I bought my project big block 454 Blazer but the previous owner made a mess of the engine bay wiring.  I'm attempting to get the original gauge cluster working but have run into a couple problems.  I found this Oil Plug connector down by the bell housing and I believe all I need to get the oil pressure reading is to hook this up to a new sensor.  This is a two prong boot connector but has three wires coming from it.  The previous owner cut the middle wire (from somewhere) and I can't find any lead that would match up to it.  Does anyone know
where this middle lead is supposed to go?