I'm not sure what Evans Wiring sells...the one I see on their page is $30?
Anyhow the white piece plugs into the big white connection block on the engine side of the fire wall. I am not sure if the grey wire goes through the firewall (it'd be easy to slip a grommet around) or if the other end (which connects to the dash light) goes through the firewall with a grommet.
For reasons I still do not understand, one of the previous owners had placed the automatic transmission harness between my transmission and the manual harness. Once I figured out that was incorrect and I removed it, I did not have to mess with the firewall portion of it.