thanks to my transmission being geared so low in my 16v I regularly hit the rev limiter. especially in 1st and 2nd.
check out the specs on this chip here
here is a quick mockup of the circuit required. its not complete, but it will give you an idea of how this works.
the important thing is how do get the signal from the tach to the signal input on pin 5 in a useable form. it might be as simple as hooking it up the tach signal line coming into the cluster - (T7b/4 R/BK) - sort of like a dwell meter, but it could require a bit more finesse than that.
the first step is go go hook up an analog volt meter to the pin 4 of the cluster connector T7b, and run the car to see what kind of signal you get there. since my engines in peices right now, someone else will have to do that for me.
either way, I will work on this more later when I have some time.
in the mean time open your bentleys to the Main wiring diagram pages and look at these pages for some light reading.
97-2541 coil and ICU
97-2544 tach + upshift control
and under electronic engine controls for 16v rocco 87-88 page 4 of 4 (97-2367)