Where do you connect a tachometer to check the Revolutions Per Minute at an idle

There are 5 wires running to two separate plugs, which one is negative, and do I pierce the wire?

The white wire with the pnk/blk, the other white wire is a digital signal for the instrument cluster, if the tach is digital use that one.

Thanks a bunch

I was tied up earlier, No Worries.