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Mine Sweeper!
6,512 Posts
What is the Big Three (Big 3) upgrade?
The Big Three upgrade, simply put, is upgrading the main three electrical charging wires in a vehicle's electrical system. These wires are the power wire from the alternator to the battery positive, the engine block to a ground, and the battery negative to a ground.

Why should I upgrade the Big Three?
The stock big three wires are often inadequate to handle the extra electrical draw of anything other than a stock electrical system. Since the majority of us like to upgrade our trucks, we often add on to the electrical system. People that see the most noticeable need for the big three upgrade are those running aftermarket lighting, just about any stereo setup that includes an amplifier, those running compressors, e-fans, ect.

Upgrading the big three often solves many people's electrical shortcomings by decreasing the resistance to the flow of electrical current in the vehicle's electrical system. This upgrade should always be the first step in attempting to solve electrical shortcomings (such as dimming headlights, your voltage meter reading 12v on the dash, etc.). It's by far the cheapest upgrade you can do for your electrical system. Also, if you already have, or plan on getting a high output alternator, upgrading the big three is an absolute must. The stock wiring is too small and can easily melt and catch your engine on fire. Then people like me get to come and jam a nozzle through your hood and fill your engine bay with water.

What does the Big Three Upgrade do?
Stock wiring for the big three in our engines can be as little as 8 awg wire. This was actually the case in my 1996 4.3L Jimmy. Very very few of our trucks actually came with 4 awg stock wires for the big three.

Ok, so what's wrong with 8 awg wire? Well, since no wire is 100% conductive, all wire has what is called resistance: the characteristic of the wire that impedes the flow of electrical current through it. Larger thickness (gauge or awg) wire has less resistance/impedence than smaller thickness wire. Longer wire has more total resistance than shorter wire of the same thickness. So to decrease the amount of resistance in a wire, you want to keep it as short and thick as possible. 8 awg wire is not very large and therefore has considerable resistance. If you try pushing/pulling a large amount of current through the wire, it will heat up (a form of electrical loss) and you still won't get the current through any faster (actually a hair slower because heat slightly changes the characteristics of the wire). It's like the difference of the flow of water in a garden hose and a 4" water supply hose from a hydrant to a fire truck. A hydrant can feed either hose, but the larger hose will move more water easier. An alternator can feed small wire or large wire, but larger wire will move more current easier.

How do I upgrade my Big Three?
Very simply, you upgrade the wires in the big three with larger gauge wires.

Things you'll need:
- About 5-10' of 4 awg or larger wire. The larger wire you can afford the better
- Several ring terminals for your size wire (6 usually: one for each end of each of the three wires)
- Wire brush (to clean your ground)
- Extended battery posts if needed
- Other tools as needed

First, disconnect your negative battery terminal like you should always do for safety when working on your vehicle. Next, while you have the wrench for the negative battery terminal, disconnect the positive one as well.

Measure your length of wires out by test fitting them into place before cutting. It is not a bad idea to follow the stock route for the alternator to battery positive wire so you don't get it caught in the serpentine belt or resting on an exhaust header. Go ahead and cut to length your wires and add the ring terminals.

Connect your new power wire to the alternator power location (usually the bolt on the back of the alternator where the stock wire is connected). Thread that wire through how you are going to run it to the battery and connect the ring terminal to the positive battery post.

If you need to use post extenders, now is the time to add the positive one.

pic of side 'post' extender:

My alternator with the engine block ground on the front of the alternator:

Now you need to focus on your grounds. As usual, a ground at the frame is best. The frame is conveniently located almost directly below our battery trays. You have no excuse not to use it. Especially since you can use the bolt location for the tow hook on the passenger frame rail so you don't even have to do any drilling. Even if you don't have hooks, the holes should still be there. Make the metal shiny before you bolt the ground to it. Then take that ground up to the battery negative terminal. Now your battery is solidly grounded. Note: you can ground to the body/chassis but you must scrape paint away until you're on bare metal, but the frame is still the preferred method.

My OLD 4 awg frame ground (it's now 1/0 awg)

Now for the third and final wire: the engine block ground. Basically, find any bolt on your engine that you can safely (don't be stupid) bolt a wire to to ground the engine block. Don't use the alternator power wire (that defeats the purpose and will short your electrical system and cause a fire once again). The easiest bolts to use are the ones holding the alternator to the bracket or one of the bolts holding the case of the alternator together. You can run this wire either to the battery negative terminal or directly to the same ground location on your frame as the battery negative to ground. Either way is acceptable.

Ralphie's entire big three complete:

He chose to ground to the chassis (I still strongly recommend the frame but this is OK). You can see his extended battery posts in this picture too.

Picture of alternator power wire and engine grounds courtesy of Joe (Paint Toad). He's using two engine grounds (one to frame and one to battery) as a little bit of overkill, but it isn't a bad idea.

Some notes
1) Fuses are NOT necessary. Fusing the power wire is pointless because power flows from both ends (either battery positive terminal or the alternator)
2) You do not have to disconnect any stock wires and it is actually recommended you leave stock wires in. Unless you're sure you know what you're doing, leaving the stock wires in is not a bad idea. You can take them out if you'd like, but it is not necessary. Your choice. Just don't let them dangle around inside your engine bay.
3) This upgrade takes about 30 minutes if you comprehend what you're actually doing. All you're doing is replacing three wires with larger wires basically.
4) Leave a little slack in the wires. The engine moves within the engine bay.
5) Use dielectric grease on your battery and wire terminal connections when you bolt them to parts of your truck to help prevent corrosion and help maintain a better contact.

Feel free to PM me if you have any questions.

Also, here's the link I learned from in case I've failed to explain this well enough

drunk and bored
31,626 Posts
just wanted to add a picture of the frame to cab ground.(temp)

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