I have a 2007 Audi A4 2.0T and I was wondering what the best way to run the + power cable from the battery to the trunk of the car.

Should i drill a hole or is there already one that I can use?

Also, what is the best way to actually run the wire from the drivers compartment to the trunk?

 

While I haven't done an install in an '07 Audi, there's typically rubber grommets in a car's firewall that allow various electronics wires to pass from the engine cavity to the inside of the car. In all previous installs, I've simply lanced one of those grommets and fished my power wire through that.

As far as getting the cable to the back of the car, it isn't really that difficult. You can use a pry-bar to lift the plastic door edge covers. These are located on the floor at the edge of your door, separating the carpet from the outside when the doors are open.

I would STRONGLY advise putting your power wire in that location, and possibly pushing it down under the carpet a bit, so that it doesn't create engine noise in your speakers.

If you're not sure what engine noise is, it's a small whistle that comes from your speakers. It is lower pitch when your car is at an idle, but squeals higher and higher depending on your car's RPM. It's INCREDIBLY annoying and will make the best audio system sound like an oldie-time transistor radio.

If you're adding all after market speakers, here's a trick to eliminate engine noise. Never run power cables parallel to speaker wires. The magnetism caused by power cables is the direct cause of engine noise. Always cross your power cables at a 90 degree angle. Your best way to hold wires in that shape is to put a bit of electrical tape around any 2 crossing wires to maintain that angle.

Remember, + is good, || is bad.

With that in mind, if you're redoing the speakers in the entire car, put all of the speaker wires down 1 side, then run the power cables down the other.

Speaker wire ISN'T length-specific. If you have a 3 foot wire and a 20 foot wire, it physically sounds the same. You wouldn't need to make a 2nd 20 foot wire to handle the 3 foot length.

The reason for this is the travel speed of electrons through the copper wire. It's only after a 1000:1 difference in wire length that you'll notice a delay in sound, and even then it's only a 10th of a second or less. But it would be enough to be annoying. (that's why concert speakers are usually off a bit)

Anyway... I hope this wasn't too much info for you. If you have any questions, feel free to ask.

 

do you know of anywhere that does this type of install for a reasonable price? I've been looking at the engine bay and found some rubber grommets but I'm still just not sure where they will come through to the cabin...

Also I have an aftermarket head unit; do you know if disconnecting the negative connection to the battery will reset the head unit (and i will have to re-enter the security code, which i don't know)?

Also I found the wire cluster going from the battery to the head unit, is there anyway i can use that same set of cables to power my amp? The cluster seems to go through the engine bay under the ecu and through to the drivers compartment and to the head unit.

 

Ok, let me handle these one at a time. The most reasonable price you'll find is if you have a friend that knows how to do it. They'll definitely charge less than a real store. Unfortunately, you may not have a friend that knows how to do it, so just bite the bullet and take it to a shop if you're uncomfortable with doing the work yourself.

Removing the power "constant" wire (yellow) from an after market head unit will 100% reset it. With that in mind, you'll have the same issue when you remove the battery terminals. You realistically only need to remove the positive (red) cable, but most people suggest that you remove both, then once they're disconnected touch them together to remove any sort of built up electrical charge in your car. As far as the security code, that only exists with OEM radios but you'll only get that flag if you physically unplug all of the connecting wires from the back of the radio. Removing the battery alone won't cause that.

No, 100% not. Amps require a LOT of power. Your car's radio, however, does not. The amp power/ground wires will likely be 4 to 8 gauge. Your car's wiring system typically relies on between 16 and 24 gauge. Take a look at this picture to see what the difference is in wire gauge thicknesses.
http://upload.wikimedia.org/wikipedi..._%28PSF%29.png

 

Oops, double post.