Can I run cable thru the firewall?

[mountainbiker]

Cable
I am hoping to get an opportunity (weather permitting) to install a HitchCAM (receiver hitch type) next weekend. It comes with a 4-wire cable. The part that attaches to the monitor has an S-video (type) connector on it.

Do you think I can squeeze this cable thru a pre-existing hole in the firewall?

Can you give me an idea where a pre-existing hole might be located?

Or did you run your cable thru the interior (if so where was your entry)?

Monitor
The HitchCAM has a 3.5" monitor with a typical windshield rear view mirror type mount.

Has anyone used a different mounting location for theirs?

The reason I ask is that we tend to have problems with people stealing portable GPS units that are displayed in the window. If I installed the monitor in another location, maybe it would be a tiny bit less visible.