Big Three Wiring Upgrade - 2nd Gen Tacoma - Writeup with pictures!

I followed this write up. Sounds like you’re headed that way. I have a high output alternator.

http://www.bodenzord.com/archives/477

 

Taking a gander at everything on this site. A lot of cool stuff. I come from a technical/mechanic background so I like to hit all the tech areas to find new ideas. Looking through this thread I can see a valid reason for the wire that comes off the alternator not being fused when rerouted to the battery. The fuse in the under hood fuse box looks like it is rated either 80 amps or 130 amps depending on which alternator is installed. If one were to install a bigger alternator, but still keep the same wiring from the fuse box to the battery, then when a winch or say stereo amp were drawing a large amount of current, it could blow the fuse or damage the wiring from the fuse box to the battery. While I agree we want to keep things protected, and there is a concern for "what if" something were to short out the alternator wire, you already have that concern if something were to short out the even longer starter wire. The wire from the battery to the starter isn't fused, and it always has power to it. Same risk there.

 

If you run a larger alt, you would either need to replace the alt fuse in the fusebox with a dummy and install an appropriate inline fuse, or run a second cable from the alt to the fusebox input with an appropriate inline fuse.

 

I can see how that would look like a viable solution, but if one had a bigger alternator, and a higher load on the system, the factory wiring from the fuse box to the battery would melt because it is too small. It is designed for a fused control of 80/130A. Even a larger fuse wouldn't fix the problem. As mentioned, even the long starter wire doesn't have a fuse on it either, and I have never seen in my shop a starter wire that shorted out on anything. Hopefully not stepping on any toes. I'm new here. Still figuring things out.

 

Not stepping on toes at all.

The starter is fed directly from the battery (giving you the full CCA rating of the battery), not the alt, so the question of the starter needing a fuse is moot.

The battery and the 12v busses in the fusebox are fed from the alt through the input fuse in the fusebox. Aftermarket parts pulling higher amps from an aftermarket alternator would need to be pathed appropriately (from a separate distribution block for example, but the possibilities are limited only by imagination). Since the fusebox is still fed by the notional aftermarket alt, it would need to be fused appropriately since it too is fed from the alt, regardless of where the high amp aftermarket accessories are fed.

The factory equipment would not be drawing more current than the factory wire can handle, so the internal wiring of the fusebox is not an issue assuming that the high-amp accessories are not being fed through it.

 

OK. I'll see if I can explain what I mean the best I can. Just trying to give clarification. The alternator wire that for example is capable of 300A on a big alternator according to factory wiring goes to the fuse box, through the fuse, then on a wire from there to the battery. The wire from the fuse box to the battery, which is used to charge the battery, is not capable of handling 300A of current. Let us say you have a 9000 lb winch that is drawing 900A of current that is, as should be, connected directly to the battery. When you are winching with that kind of load, the 300A alternator is going to go full-power to try and maintain charge the best it can. The small wire from the fuse box to the battery can't handle 300A of current, so it melts. With the alternator output sent directly to the battery, this would not happen. One could see the possible desire to have a 300A fuse right at the battery for it to be wired this way, but why? The starter wire is just as much at risk of being shorted out as the alternator wire when wired directly to the battery. I hope I explained myself well enough to be understood. Kinda long winded.

 

This thread - https://www.tacomaworld.com/threads...headlights-custom-winch-runs-and-more.712981/ - might explain some of what you're asking about. The installation referenced in this thread is bad for several reasons, and the thread I just linked includes detailed explanations and circuit diagrams of the Tacoma's wiring.

 

I was reading your well-explained write up, but it still fails to take into account the situation I mentioned above, when having a higher output alternator, and a winch, with the factory power wire from the fuse box to the battery itself. At least I didn't see it myself when reading. Can you clarify?

 

You would need to upgrade the wiring path to handle your current. That writeup clearly details upgrading the factory fusebox to battery run.

 

So I still don't see how that is really any different than the above kit the guy installed where the alternator goes straight to the battery, and then another wire goes from the battery to the fuse box, allowing the fuse box to retain it's original fuse.

 

The "above guy" is cutting the alternator fuse out of the fusebox path, meaning that the fusebox input has no fuse at all, and everything in the fusebox is at the mercy of your alternator not shitting the bed or a battery short.

This is explained very clearly in the thread I linked, complete with circuit diagrams.

 

I get that you have a greatly detailed explanation with diagrams and everything. I have read it. But you are incorrect in your assumption that the fuse box input is not fused. The above kit wires to the exact same place that the factory alternator does to the fuse box. It just simply first routes that power to the battery first, then down to the fuse box. The vehicle wiring is still just as protected as it was with the factory wiring against the alternator "shitting the bed" so to speak. The writeup you mention does essentially the same thing, but instead of alt-fuse box-battery the other setup is alt-battery-fuse box. Both still have the factory wiring protected.

 

You are incorrect about how the above kit routes.

 

Using this photo, and what I have read, it looks like that highlighted wire goes to the fuse box where the original alternator went. Then the shorter of the two larger wires goes to the alternator. Sorry, I don't see what I am missing here.

 

The top stud of the fusebox feeds the 12v bus in the fusebox through the alternator fuse. The battery feed is on that bus.

By feeding the battery directly from the alternator, and rerouting the battery feed wire to the alternator input stud, as in the setup in this thread, you are 1) removing alternator fuse protection from the battery, and 2) providing an alternate path for the alternator that bypasses the alternator fuse, and bridging it directly to the 12v bus bar inside the fusebox.

The battery is not meant to be fed directly from the alternator.

The 12v bus is not meant to be fed directly from the alternator.

The fusebox nor the alternator are designed to handle the CCA load of the starter, which is also provided a direct path to the fusebox bus in the setup in this thread.

The battery isn't "first" from the alternator to the fusebox, it is in PARALLEL in the setup in this thread, because the grounds are all common.

I hate to sound like a broken record, but this is explained IN DETAIL in the thread I linked, to include circuit diagrams and photographs that show how and why this happens with the setup in this thread.

 

I can see what you are talking about, but in the above designed wiring that I quoted, the power from the alternator going to the battery, then routed back to the fuse box where the alternator fuse is located, still uses the alternator fuse to protect the fuse box. You are not bridging it directly to the bus-bar, unprotected. It still goes the the exact same terminal that the original alternator wire went to.

"The battery is not meant to be fed directly from the alternator." There is absolutely nothing inherently wrong with it being wired that way. It allows a higher output alternator to send power directly to the battery, were the larger loads of a winch or other high current item to draw power from, which is the way it should be. There is absolutely not enough wire size from the fuse box power connector to the battery to handle higher current.

"The fuse box nor the alternator are designed to handle the CCA load of the starter, which is also provided a direct path to the fuse box bus in the setup in this thread." I never implied this, so not sure why this was mentioned?

Look, I get it. Your description is well written, and you are not sounding like a broken record at all. We are just civilly debating wiring and current flow. I taught automotive technology and in most detail drivability and electrical systems, so I get your write up. But still in the write up it doesn't explain, that I can see, how the fuse box and wiring from the fuse box to the battery is protected with a 300A alternator and a winch under load. Because it isn't if the alternator output goes to the fuse on the fuse box, then from their through the factory wiring to the battery.

 

The battery feed wire is looped back around to the alternator stud in the above writeup to provide voltage information to the vehicle systems that require it.

 

So you are saying that there is a wire that you add that goes from the stud on the fuse box, directly to the battery?

 

No, from the factory there is a wire (called in various places in these threads the "under the fusebox wire") which originally feeds the battery from the fusebox. Big 3 kits of the kind shown in this thread and a few others take the battery end of that wire and loop it back up to the alternator input stud, so that the factory systems that expect to see the battery voltage on that wire will still do so after the changes to the alternator and battery routing.

Here are the relevant portions of the writeup in this thread that illustrate what I'm talking about:

As you can see, this bypasses the alternator fuse that sits between the alternator input stud and the 12v bus in the fusebox.

 

OK. I can see what you are talking about. So it's really a matter of the way that particular wire itself is routed, and not the actual wiring kit itself being designed wrong. We were both looking at things from opposite ends of the spectrum. The wiring kit design isn't bad, just how that particular wire from under the fuse box is routed.