So you just got your system in your car and the headlights are blinking hella bad when you got the bass going. Your thinking of a cap but somebody on this forum told you they were crap and said upgrade your Big 3. "What the hell is a Big 3?" It's a great way to get all the power you can get from your charging system to your amps and the rest of the car. Its a simple mod to do and shouldn't take you much time to do if you have all the tools.
You use huge power/ground wire to your amps to get the most power right? What most people don't realize is that coming off your alternator is a big phat (note sarcasm) chunk of 8 gauge cable crimped to a shitty (and probably badly corroded) ring terminal. If you think thats bad...the thickest ground wire is a 10 gauge piece to the engine...and the body ground might be a 10 gauge if your lucky.
The concept is simple and straight forward. You upgrade your alternator (1), body (2), and engine (3) cables to a more substantial size. This lets you pass a lot more power to your battery and electrical system. It also lets you use better terminals and freshen up the likely corroded spots where the factory grounds were. lets get started...
First things first. How thick do you need to go? I've always used a minimum of 4 gauge cable. If your audio system is using 8 gauge its likely not powerful enough to dim the lights...if it is your either using power cable thats too small to begine with or your problem lies elswhere. If your going nuts with the system then by all means go with thicker cable. The car in this FAQ is done with 4 gauge. I've actualy done a bit more than the big 3 in this one though....
Next up is making your power/ground cables. This is something that is easy do and easier to do a crummy job on. Your goal is to make a cable that is going to last a long time. Gold terminals are nice to have and expensive as well. Try to find them cheap. If you can't find any you can get copper ones from most parts stores but they are more likely to corrode. You can paint them after they are tightened to seal them up better from the elements.
Squishing a terminal onto a piece of 4 gauge with pliers and wrapping it up in tape is a good way to run into problems down the road. You want to crimp the ends on with a vice and then solder the joints with a torch. Don't use a soldering gun to solder 4 gauge..it'll never get hot enough to solder properly. I also use flux to help draw in more solder to the joint. Be careful with the torch as it heats the connectors up very quickly and can melt the jacket on your power wire. Basicaly I crimp the terminal in the vice and solder the exposed wire. After it cools I slip a piece of double layer heat shrink over the end. I highly recommend double layer BTW because it has a glue on the inside that seals the connection from the elements. Do the soldering right and cover it with double layer shrink and it'll last forever. This is what the connector should look like after your done:
Measure out the lengths you need and solder the appropriate connectors on. I did a piece on the engine, transmission, and body. You don't need to do the transmission ground but I like overkill. Its easier to get the trans ground with the battery tray out. This gives you the oportunity to clean out all the crap that will be under there. This is the trans ground and the next pic is the body ground. You can see some bare metal in the body ground pic..this is going to get a dab of paint to seal it up and prevent rust. I also use a dielectric grease on all the mounting points. I haven't done the power wire from the alt to battery yet so there is no pic of it.
Thats it for the big 3. Its really a good mod to do even if you don't run a huge system in the car. You could upgrade the grounds to 8 gauge and leave the power wire alone. Healthy grounds make your electrical system really happy.
I did go a little further with this one though. I also upgraded the power wire to the engine fuse box to 4 gauge. You don't really need 4 gauge but its all I had handy. 8 gauge would be more than enough. Its a little more involved because you have to take the connector apart and splice a piece of 4 gauge onto the factory 10 gauge piece. Mine was in really good condition with no corrosion so I didn't bother to get a new connector. If you have bad corrosion you probably should replace the connector first. The connector can be a pain to get apart but you need to do it or you will melt the plastic. I left about 1/2 an inch of the factory wire attached to the connector. I soldered the wire to the connector first and then soldered it to the piece of 4 gauge I had. Covered it with the heat shrink and then stuck it back into the plastic piece. It was a bit of a pian to get it back in with a 4 gauge piece. * gauge would be a piece of cake. This is what the wire looks like when your done.
This is the wire plugged back into the fuse box..
And this it the wire tied up waiting for the battery to be put back in...
BTW...you can see in the pic that there is some dirt by the hole where one of the battery tray bolts goes. This car has never seen rain or snow...gets driven 2-3 times a month...and it still manages to get dirt up there. Imagine what a daily driven all season car has under the tray. You'll get a chance to clean under there if you do this mod...so thats a free bonus
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This is where the alternator wire connects. As said before leave the factory wires there. The piece you add is there to supplement the factory wiring. Make sure you tighten it up nice and snug. I wrap my ratchet in electrical tape just to make sure I don't ground out somwhere with the ratchet handle...if you do it once you will remember to never do it again
Last but not least you route the wire to the battery and make sure its all nice and secured.
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a solid grounding wire will definitely help with starting but it sure won't increase your charging voltage by almost 1 volt, your charging voltage is dependant on alternator speed and the state of charge of your battery.
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Only I went overboard and did 4ga power and grounds 
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