Audi Repair: 96 Cabriolet Oil Pressure Light/p0116, aftermarket radio, aftermarket stereo

Question
Hello,
I have two issues with my Cabriolet:
1: The oil pressure light blinks for about the first 2 minutes of driving.  It does not blink if I start the car and allow it to idle for a few minutes before driving, but when I start it up and go it blinks.  It only happens when it is cold. Pump?  Where is the sensor located?
2: Check Engine code P0116 related to the ECT.  I know this code can be related to the sensor being bad, bad ground, or a faulty ecu. I don't know how to test or locate any of them.  I'm hoping to sell the car so I don't want to shell out for a factory manual, but I'm finding it difficult to troubleshoot/locate components without one.

Finally the radio doesn't work and I was wondering if I could replace it with an aftermarket stereo or oem would be required because of amps.
Thanks-Luke

Answer
I would check the oil pressure sensor, did you change the oil?  An oil and filter change is the quickest way to establish if the problem is real.  Regarding the coolant sensor, this is a high failure item so I would change the sensor and see if that takes care of the problem.  You can fit an aftermarket radio in these cars no problem.  Let me know,  Jan