one the lights up in the dash when you hit 2k on the tach? Other then that it never comes on. Not at Start-up, not idling, not when just cruising. Only when I hammer it/accelerate from a dead stop. I am aware there are 2 sensors on a T piece around the Oil Filter/Cooler part. One faces to the front & another faces to the rear. Which one is it? And how hard to replace?

 

On the Audi 90 without oil gauges these switches are mounted above the oil filter and behind the oil cooler. One switch faces the front of the engine, and the other faces the rear of the engine.
1) The front facing switch (white or black body, single tan or white/gray wire , Part number 056919081E ) is the high pressure switch. It is normally open to ground, and is spec'd to close at 1.8 ± 0.2 bar (26 PSI). If engine RPM is above 2000 RPM and this switch remains open, the ECM senses less than 26 PSI at 2000 RPM, and after a two second delay the light and buzzer should come on. Once this switch remained while RPM's are over 2000, the light and buzzer will continue regardless of the engine RPM until the switch closes to ground.
2) The rear facing switch (blue body, single blue or blue black wire, Part number 056919081D) is the low pressure switch. It is a normally closed to ground, it is spec'd to open at 0.3 ± 0.15 bar (4.4 ± 2 PSI). It may be marked "WK" ("Wahrning Kontraption" in German). Any time the wire is grounded, the warning light should come on. If this wire is disconnected, there should be no light, even with key on, engine off. Any time this yellow wire connects to ground, the oil warning indicator should be on.