*cough*cough* big 3 *cough*

keep_hope_alive said:

The Big 3 reduces voltage drop due to current draw on the factory wiring.  It does not increase the output current from the alternator which inevitably determines operating voltage.  if dimming goes away when the engine RPM are around 2000 but appears at idle then the issue may be simply due to the system exceeding what the alt can provide.  A volt meter is handy for this diagnosis. 

Factory grounds are usually undersized so those are the highest priority.  The factory alt wire is likely 4awg but it will have a better insulation than most aftermarket wiring so the insulation may be thinner, thus making the wire seem smaller.  OEM wire adheres to ASTM standards while aftermarket wire does not.  

A second run of 8awg from alt to battery can improve current delivery by reducing resistance but only if the connections are really high quality.  There is usually more resistance in the connection than in the actual wire.   Adding a second alt wire usually means compromising the protective boot, letting water and dirt get at the connection.  All that is to say that adding a parallel connection cannot make the total resistance worse but gains may be minimal if not properly executed.  Additionally, connections with resistance generate heat (because resistance dissipates heat and consumes power).  Lastly, I recommend fusing the alt-batt wire at the battery, as any battery connection should be. 

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