I bought a 120 amp alternator for my 86 4Runner, and i will be upgrading the wiring from the alternator to the fuse box and battery, but i want to make a few changes, so tell me if this will work. I plan on running 4 gauge wire from the alternator directly to the battery, and then from the battery to the fuse box, using the 80 amp fuse in the fuse box as the fuse between the battery and fuse box. Will that work or will i need to upgrade the 80 amp fuse to something bigger ?.

 

As long as you don`t draw more then 80 amps you will be fine.

If you do then you will need to go a little bit bigger if you figure your max current draw and fuse according to them

 

I just keep thinking that i need to upgrade the 80 amp fuse to a 130 amps minimum, because the max output of the new alternator is 123 amps at 5000 rpm. im still looking for opinions.

 

That's how I have mine set up, you'll also want to throw about a 150 amp fuse in the alt to battery wire.

 

Ok, so it would also be a good idea to add a fuse between the alternator and battery, i wasn`t going to do that, but it does seem like a good idea.

 

Don't forget to upgrade the grounds...probably the most important imo.

 

I already have the wiring to upgrade the grounds, so i will be doing everything at the same time.

 

I would probably do things a little bit different. If you take the fuse box apart, which is really easy you can see how everything is wired from factory and I would follow that. From the alternator it runs into the fuse box to that main fuse, from that it runs to the battery and to everything else. So if you're running it directly to the battery that fuse is doing nothing. If you unscrew the few screws from the box and flip it over, the bottom pops off, you then have access to the main fuse and you can unscrew the old cable, buy yourself a 4ga ring connector and screw it on to the main fuse, at the same time you can replace it with a 120a one.

120amp fuse should be more than sufficient. You have to remember amperage is only there when it's needed, and I seriously doubt you'll be needing more than 120amps. I say 120amp fuse because I think that's what NAPA has, I bought the biggest one that had, 120 or 130, whatever it was.

Edit: One other thing you'll need to remember is to keep one end of the old cable connected, if you disconnect both ends of the existing alternator cable it won't start, there is something wired in line somewhere that is required to be connected.

 

The way i planned on doing it was to run the wire from the alternator to the battery, with a high amp fuse in between, then go from the battery to the fuse box, using a 120 amp fuse between the battery and fuse box and completely remove the stock 80 amp fuse.

 

where did you get the alt from?

 

I've had a 140 or 160 amp (i forget which) in my '88 3VZ from a lexus for over 10 years now. All I did was run a new 4 gauge wire from the main lead from the alt to the battery postive top post. (leaving the factory one in place as well)From there I put a break-out fuse block (on of those gold stereo fancy ones) off of the battery. I did not bother running a new wire to the factory fuse box since all of the high draw accessories like stereo amp, etc. now feed from the block directly. Also when I hook up my winch it goes directly off the battery. So unless you plan on running new high-draw accessories through the factory wiring/fuse block there is no reason to upgrade the wire there.

 

This sort of thing is how this happens:



Do not change the 80 amp fuse out. You can run a larger gauge wire from the alternator to the battery, as that is how the factory system is set up now, just cleaner.

 

The alternator im using is for a 90-92 MR2 (i believe that`s the right year), i bought it new. Someone here did a write up on installing one on a 84-88 truck/4Runner. im installing it on my 86 4Runner

 

If i make no changes to the wiring can it handle double the amp load, going from a 60 amp stock alternator to a 120 amp alternator ?. When ive been at pic n pull looking at alternators on cars with higher output alternators, like a Lexus, the wiring doesn`t look any heavier than what`s in our trucks ?.

 

X2 do not change the the 80 fuse
Remove the old wire from the alternator to the fuse block there should be another wire that makes a T conection to your power wire around the side by the air intake connect that one to your big wire and i recommend a fuse there too, now in the fuse box, open it up and take the old wire from the alternator and leave the 80 fuse because there is another wire there also in the side that comes from the alternator,
now your big wire runs directly to the batt and then from there you should have a stock wire running to the fuse block.
You dont need to upgrade anything else besides of the grounds because everything connects to the battery

Also that big power wire needs its own fuse, and you fuse according to the wire size not alternator output

 

If you can do it, do it it might handle the power but also with bigger wire you get less resistance and less drops under heavy load

 

The truck itself is not going to pull more through the fuse box than what the stock fuse is rated for, no matter what alternator is installed. If you think about it, there's really no reason to change the stock alt fuse to a higher one at all! You're installing a higher output alternator to do what; keep the battery up because of other electrical accessories that are not stock (lights, electric fan, winch, air compressor, etc.). When you install those aftermarket electrical accessories, where are you pulling the power from? Typically, you take the power DIRECTLY from the battery terminals, or from a separate installed fuse block that is fed directly from the battery terminals. So those installs completely bypass that alt fuse in the fuse box all together, and do not put any more load on it than there already is from the truck.

What I WOULD do is add in a second line from the alternator output to the battery, and make up the other 60 amps there with an inline fuse (leaving the stock 60 amp fuse in the stock location, and installing a 60 amp fuse in line between the new alt and your battery with your added on charge wire), thus giving you the ability to take full advantage of the 120 amps that the alt has to offer

 

If you look at how the alternator is set up now, you have a 60 amp stock alternator and an 80 amp main fuse in the fuse box, so they use a main fuse that`s rated 20 amps over the max output of the alternator. So if i install the larger alternator and leave the stock 80 amp fuse, it will blow as soon as the alternator pulls over 80 amps. So if i ran larger wire from the alternator to the battery with its own seperate fuse, that would eliminate the power from the alternator going through the fuse box, and if i kept the power wire from the battery to the fuse box it would still use the 80 amp fuse, but the output from the alternator wouldn`t be going through it. would that set up work with out any problems ?.

 

That explanation slightly threw me off, but I think I understand what you're talking about, lol. Yeah I'd leave the stock fuses alone and just install the extra wire with the in-line 60 amp or so fuse at least, that's what I would do were it me... I'm sure other's might have another opinion

 

Im leaning towards leaving everything stock and just adding the heavier gauge wire, but your throwing me off by saying to add a 60 amp fuse, won`t that be to small ?, don`t i need a fuse thats rated at or above what the alternator puts out so it won`t blow when it see more than 60 amps ?.