In post #3 I posted a link to the Audi World version of the link you posted. We already knew the wiring, but needed further clarification.

 

Hi jeckel, thanks for chiming in, I appreciate it. Like MetalMan said, the pin in the cluster was listed in that other thread, but since I won't be using the B5 cluster, I needed to know which wire triggers the CEL coming out of the ECU so that I can incorporate a new CEL into my cluster. With the Bentley incorrectly listing the CEL as the Trailer Operation Indicator Light and labeling it K18 instead of the typical K83 normally associated with the CEL, this left some confusion. Since the Bentley is incorrect concerning the CEL at the cluster, it was hard to know (or trust) if it was correct at the ECU. But thanks to MetalMan, we now know for sure. Thanks again!