General housekeeping rules when installing a sound system:
1) Run the power cables and the RCA cables on separate sides of the car.
2) The remote cable (usually blue / white stripe) runs from the HU to tell the amp to turn on. This cable is usually attached to the RCA cables in your amp wiring kit. Detach it from the RCA's and run the remote cable along side the main power cable.
3) The Coupe does not have a switched ignition wire to the HU. Simple solution was to spliced the HU switched live into the cig lighter switched live (red / yellow cable).
I've recently installed a second amp in my car and had two problems.
Alternator whine - caused by a ground loop.
This was a loud whine in which increased with the speed of the engine. A ground loop is when more than one earthing point is used in the car.
To remove this problem I applied the following:
1) Tightened the ground on the amp
2) Increased the amount of ground cable which was in contact with the bare metal of the chassis.
3) Ran a separate ground wire from the amp and spliced it into the ground wire at the headunit.
Speakers popped with the ignition turning on.
This is caused by the amps getting power the instant the ignition is on, rather than when the HU is turned on.
The problem was I spliced the remote cable into the cig lighter ignition switched live. I removed the remote cable from the cig lighter ignition switch and used the correct cable from the back of the HU.
Now I have a whine and pop free set up.
It took me a few days of searching to find the solution to these two problems, so I thought I'd post them up for all to see. This website was very helpful.