The pink wire shows in my manuals as a common 12V+ looping through the dashboard to various components including the tacho and is fed from fuse terminal 11 but this is from a HZ Monaro/GTS. The HX Monaro/GTS doesn't appear to have this pink wire connected to the tacho. Black is an earth wire and brown heads off to the negative side of the coil.

HZ Tacho wiring. (86 = Tacho, K = Pink, B = Black, N = Brown)
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HX Tacho wiring. (87 = Tacho, No pink wire shown)
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