Location AC Low Pressure Suction Value

Hi Everyone, Just purchased this great car 92 MGM with less than 76K miles on the clock :-) it has the normal paint issues for that year, and I am getting 24 miles per gallon. What I need help with here folks is this,
1. Where is the low pressure suction value for the A/C system? I have checked and found the high pressure value in the engine area(it also had a red cap on it). Is it located under the dash, on the passanger side, up behind the bottom panels that hide everything? Just trying to ovoid tearing everything out in order to find it.

2. I want to install a tach on this car to monitor the RPM's, also Oil pressure, Water Temp and Battery, What would be the best locations to hook up from(wires and sending units from standard points or otherwise) and the safest. Would I be piggy backing off the sensors there or what?
Any and all help would be greatly welcomed for this great car. Bob

The Low Pressure Cap is located on the side of your Accumulator, the black container by your coolant. It should be a cap on the side of it

Thanks Uno for your help, I will look for it. Any furthur help on the other part of my question?

No, sorry man. I'm no good at that stuff