The red wires are attached to numerous places around the chassis engine and the battery. It's to help with the earthing.
"Better grounding increases the signal-to-noise ratio across the board for the scores of electronic sensors feeding real-time engine information to the car's ECU (electronic control unit) — especially for high-frequency, performance-critical inputs like the oxygen and mass air flow sensors. Simply put, faster and better ECU decisions translate directly into improved engine performance
But that's not all. Added benefits include more immediate throttle response at all engine speeds and, according to one dyno test*, an extra 5 bhp at 5,100 rpm and 6 ft-lbs of torque at 5,400 rpm, with lesser gains throughout the power curve. And all this for under $30 if you do it yourself! You'd be lucky to get gains like that with a cold-air intake and cat-back exhaust costing over $1,500 in parts alone
Bottom line: I highly recommend this simple but highly gratifying modification. The claimed benefits— increased engine smoothness, responsiveness, power and torque— are real and noticeable, and the cost and effort are negligible. I used to be able to feel 6,000 rpm coming, but no more. That programmable "up shift" warning light now earns its keep
Taken from:Turbo & High-Tech Performance Magazine, July, 2003 - Nissan 350Z
If anyone else would like to do this quick and simple mods to their vehicle, it can be viewed here: http://www.z-xtreme.com/350z_Instructions.htm
I bought this as a private sale from Japan which took me over 6 months of continuous searching through auctions etc to find a 15 year old GT-R in as good conditon as this one - there is a lot of high km GT-R's in poor condition with very little mods out there