[s-cars] An S2 problem

[c cohen]

Anyone know why an RS-2 engine installed in a 1991 Coupe Quattro.which has the RS-2 ecu, also has an immobilizer that is wired to something in the instrument cluster 
of the original cars. The signal received from the instrument cluster trips the immobilizer allowing the car to run. I need to find out how to either bypass this signal or obtain whatever it connects to allowing the car to run! There is a 1995 S-4 chip installed now which makes the car run but the programming does not match the engine and would like to return to using the RS2 chip.
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Any ideas?

Colin