nearly done, few straggling wires to sort out

1. What is the pressure reg solenoid, i have a plug for it but not sure where to find it

2. G/OR 44 wire from ECU is labelled "neutral switch" in my diagram, should it just be permanently earthed or powered or other?

3. Y/R 7 "tacho drive output" can this be simply connected to the 1200 original tacho?

4. ECU pin 5, light green wire "boost control solenoid" what should i do with it?

5. i have a brown wire coming from the engine side of the loom, looking at the wiring diagrams i have it seems there is a brown wire which powers a few of the sensors, sound right? just connect it to IGN power?

6. (not a wiring question) what have people used for the O2 sensor? i need to get a sensor from somewhere