Has the harness been changed to a 71 wiring harness? It looks identical to the 70 harness for a conventional cluster but if the harness is for a rallye cluster the wires in the master plug will be arranged completely differently. I haven't found the arrangement to the rallye plug but there here's the info referenced by '63GT. I printed these out for my usage when i did aftermarket gauges but a FSM is really your best friend here.
The guy I bought the harness from said it was a 71. From what I’ve been able to tell through all the wiring diagrams I’ve printed, he was right. But to me those diagrams are like trying to read an ancient Chinese scroll lol
