Multiple smaller gauge wires for alternator B+

I'm in the process of installing a new engine harness to my gen3 3sgte. The stock harness routed the alternator B+ through a couple of plastic covers over the cam cover and round the inlet, which id like to try and retain. Instead of 1 large cable. 2 x 10 or 8awg wires were used.

Would it be possible to use 4 x 12awg spec 55 wires to do the same job? (Mainly because its what I have to hand). Looking at the current sheet hpa has put out, 14awg will do 22a at 80deg c. Im hoping 4 x 12awg will do 25a each but not sure what bundling them together will do?

Once round the engine I'll probably convert to a single 25mm battery cable using a junction block or similar

You'd really need to know what kind of current you'll be pulling as well as acceptable voltage drop would be to make an accurate assessment - my kneejerk says 'sure that would be fine' but it's not really good math as there are so many dynamic variables from one project and bay to the next. This and RBRacing's info-dump of a website is what I use as my reference materials when I forget how or what to math:

I've never been a fan of running multiple wires between two common points as a way to increase current capacity...

This would mean that you would be fusing the circuit for the final current needs, and not the proper fusing for the size of wire.

I've seen this idea result in fires, especially when one of the conductors develops an issue, such as corrodes or gets damaged in some way that reduces current capacity, which then the remain wire(s) take up the slack and now they are probably carrying more current than they are safely rated for.

If each wire is fused independently, then that can work, but I RARELY see this happen.

Thanks for comments. Just for some clarification ive attached two pics of the run. The Alternator puts out a max of 80a and from factory the run is protect by a 100a fuse (see pic 3 of the stock cable pair).

The first picture shoes the run in yellow that goes through 2 plastic covers (red & blue) and the run is a total of 5 feet where I would be converting the cable to a 35mm single cable.

What I could do is:

1. As above run the 4x smaller cables for the entire 5 feet where I can terminate to either a single 100a fuse terminal, 4x 25a distribution block or stud where I convert to a single 35mm cable.

2. I can crimp the 4 x smaller cables into a closed barrel terminal to a single 35mm cable and have the crimp in the blue cover which would reduce the run of the smaller cables to about 2 or 3 feet.

Why wouldn't you just run a single 35mm cable for the entire run?

To be honest for an 80A alternator 25mm (4 AWG) would be plenty, even a 16mm (6 AWG) would suffice, especially since you'll likely never see a full 80A output, and if you do, it would only be very briefly.

Just for reference 2x10 AWG is about equivalent to 1 7 AWG (little larger than 10mm^2), 2x8 AWG is about equivalent to 5 AWG (little larger than (16mm^2), to go back to what you had mentioned in your original post.

As im tryibg to keep the install as neet as possible, i want the cable to fit in the plastic covers that sits on top of the cam cover, (the one marked in red on my pic.

A single large gauge cable is too big to fit in this cover along with the portions of the engine loom, which comes down the front of the engine. That's why toyota must has split it into 2 smaller cables. I could do the same but I happen to have a lot of 12awg spec55 spare so I was hoping I could use 4 or even 5 if needed of these cables instead, just to save be bying anymore.

A single 6 AWG would likely take up less space than the equivalent in multiple smaller gauges.

It would take 4 12AWG wires to equal one 6 AWG...

5 12AWG is equivalent to about 5 AWG.

10 12 AWG wires to equal 2 AWG, the 35mm^2 cable you were mentioning earlier.

This is about safety, not just what might work.

The 12AWG wire at the length that you're looking at is only good for about 20 to 25A, and if you fuse it at 100A, at the battery end, like you are mentioning, you really are taking a huge chance of fire occurring, especially if one gets damaged in anyway, such as chafing, or if a crash happens and pinches the wire.

Just because Toyota did it a certain way, doesn't necessarily make it a good way.