Jim, KF4NBG, shared this on the HamRadioHelpGroup list today:
My club had a fox hunt yesterday, a group of us were standing around chatting and I mentioned that I was trying to find a car stereo system installer to route the power wiring from the battery to the cab. One of the guys spoke up and said that he installed systems in cars for 15 years and showed me exactly where to run the wire.
It seems that most if not all foreign and some American cars have an automatic transmission, but when they form the body parts they stamp out the space for the clutch pedal to go through the firewall since it doesn’t cost any more to have the hole there. He looked under the dash, sure enough the space was there and very easy to get to, he also showed me where it will come out in the engine compartment. All I have to do is drill a hole, put a rubber grommet into the hole and run the two wires.
Hope that this tip helps you and saves you a few dollars as well.