Has anyone found an easy route from the cabin to the engine compartment, to get a cable through? I looked and looked, but have not been able to find a good route. TIA

 

How about the big rubber grommet behind the battery? There are several blocked off nipples you can cut off and route wiring through there. I used one to route a power cable for my subwoofer amp.

 

Just above the brake pedal there's a big rubber grommet. You can carefully cut that open a bit with a razor blade to give you some added room to run wiring cables. We've run vacuum line as well as clean power and UniChip connectivity wiring through there on our MINIs.

 

In order to get a cable through the firewall at the drivers side, you have to pull both wiper blades off, remove the windshield right and left covers. there is a penetration there with a domed plastic cover that can be popped off. The rubber boot has two spare holes in it. The same applies on the other side behind the battery.