I have installed a block heater (Defa) and now it's time to route the cable for the coupe heater. I must go from the engine bay into the cabin through the firewall. Anyone who can give me a tip of where to suggest the location of a hole where I can route the cable ?

 

There isn´t many choices... or at least I didn´t find.
I routed cable through firewall from car´s original grommet which is approx behind original air filter box. There goes car´s own big harness too. That rubber shield was pain in the a** to slide over and make hole to it.

 

Did you have to remove the panels inside the car to route the cable from the drivers side to the pass. side ? I guess that the harness comes in somewhere around the steering column ? Where did you install the external plug ? To the left of the intercooler ?

 

Yes I remove that plastic panel under steering column so I can see where the cable gets inside the car. Then I routed the cable behind the center console to passenger side.
That external plug was already installed. It is next right to license plate.

 

*Done* Found a cable that routes through the firewall on the passengerside directly under the blower. We however decided to drill another hole close to this one to be sure that the fittings are watertight. The installation is the cleanest I have done so far.