Running wires from outside to inside car

[cobra mk8]

I’m installing a wide band o2 and would like to know where a good place might be to sneak a few wires with a small plug on the end of it into the cabin.

 

[slowmkviii]

I would say with the trans. Harness

 

[chris2523]

there is a big hole in the firewall with alot of other wires running through it already isn't there?

 

[Sapperfire]

Trans harness would probably be the shortest route

 

[DieselDan]

How about the shift cable gromet?