This may be a 87-88 issue only. Theirs 2 tan wires coming out of #1 on the A plug as circuit 657. It's still for the engine light. The 87-88 evtm list it as 657 to. not that it's a big deal.
this topic has always bugged me, I will compare two full digi clusters then compare two base electronic clusters , then compare full buttstuffog clusters to the 87 & 88 evtm and likely build a spreadsheet.
i am having trouble even with the chart your posting as it compares to the 87 shope manuals.