I don't think MulletproofMonk's oil pressure wire description is accurate. The FSM shows it this way:
Oil pressure sender pin A -> Fuel pump relay pin D -> Fuel Pump Fuse (all orn/blk wire)
Oil pressure sender pin C -> splice S509 which branches off in 3 directions: fuel pump relay pin B, ALDL pin G, and C203 pin L onwards to the fuel pump (all tan/wht wire)
Oil pressure sender pin D -> C203 pin E -> Oil pressure gauge (signal)
For the A/C, if the compressor is originally from a 4 cylinder car as you say, then forget about what I posted earlier. Here is what you need to know: there are two pressure switches located on the back side of the compressor. Each has a pair of wires going to it. The low pressure cut-off switch has a light green wire and a grey/red wire going to it, and the high pressure cut-off switch has two grey/red wires. They are wired in series meaning that if either one opens, the circuit is broken.
In the stock Fiero configuration, the power runs like this:
HTR/A/C Fuse -> A/C control Head -> Low Pres Sw -> Hi Pres Sw -> Splice S512 going to two locations ->A/C compressor control relay (coil, pin A) then from coil ground (pin C) to ECM which switches the relay coil to ground when commanded;
AND, Splice S512 also goes to a separate ECM pin to alert it to ramp up the RPM to compensate for the extra power needed to turn the compressor.
How you need to hook these up to your new ECM is what you'll need to figure out.
[This message has been edited by Bloozberry (edited 10-08-2013).]