On the block by the timing cover,which is the stock location.
The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.
my batt is in the stock location. so should i keep the ground where its at and add more coming from locations listed in the link? how do i ground the computer? thanks
is the secondary power ground a flat braided wire? should i run a larger gauge wire instead? with my batt in the stock location is there a need for the extra grounds? thanks
Often times it is not NEEDED per se, but evidently, in terms of less electrical "noise" and voltage drop from your equipment, there seems to be something to be gained from an "optimized" electrical system with regards to overall vehicle performance. Whether that transfers into more horsepower or simply less electrical noise within your audio system is difficult to say until you actually do the project.
Grounding the computer will be relatively easy. You should have at least one ground on the housing, then there should be two ECU grounds (pin 40 and 60 on a A9L) and there should be a TFI gound (pin 14?) that can also be used. Just find those grounds on your computer (using a wiring diagram) and "T" in 14-16ga ground lines to say, a 4-6ga main and run that 4-6ga line to your negative battery post.
If you take a closer look at some of those ground kit diagrams, you will see the locations and the sequence in which they recommend.
The computer ground is in the fuel injector harness. It is an orange wire that comes out at the very top of the harness. It can be grounded to the back of a head, even where the braided wire is grounded. Run a file on your stock battery ground location at the front of the block to remove any gunk or paint, and you should be good to go.
You can run it to the head, assuming your engine grounds are good. Better would be a dedicated copper line to your negative battery post or the 2ga line that runs to your battery post.