When replacing the alternator with a high output one you'll need to run a dedicated power line from the alternator output to the positive terminal of the battery. Failure to do so will pop the 140A fuse when the high output alternator delivers over 140amps.
DIY - The OMG I Blew the 140A Alternator Fu$e
- Thread starter LOLSNOW
- Start date
When replacing the alternator with a high output one you'll need to run a dedicated power line from the alternator output to the positive terminal of the battery. Failure to do so will pop the 140A fuse when the high output alternator delivers over 140amps.
rigtec
New member
Hi LOLSNOW,
That's 'EXACTLY RIGHT'! When I initially installed my "270-XP", the plan was to run a direct line from the alternator "B-term"(HOT output) to the POS Battery term, and adding a fuse to comply with Toyota's 'Fire safety provision': 140A inline fuse/circuit breaker, just in case of a total loss front-end hit!
After doing so, I realized that that's a HUGE err in judgement! If I would ever take out that "Direct Charge Line" 140A fuse; due to the much higher ampere flow to the electrical add-on's, it would not only take out the auxiliary in-line fuse/breaker, but then the extra high current would have no other option but to front travel through the stock factory 140A safety device (likely over 200 amps), and wipe it out as well!
I'm sooo glad that I noticed that flaw in the design BEFORE 'Catastrophic Chain Destruction Phenomena' could take place! Once again [MENTION=153545]LOLSNOW[/MENTION] , this was a GREAT thread, and an Awesome education for me, 'Best to you' and your loved ones, now and through the upcoming Holidays,
rig, cheers!
Live to fight another day
I'd like to thank the OP, Antman, and everyone who contributed to this. I blew the 140 installing the big 3 when the cable slipped and grounded to the engine -POP! Lesson learned - remove the battery.
I'll admit, I failed miserably! After 2 days, about 7hrs in all, and with a storm brewing, my hands and fingers sore and cut up, my back aching, and my ego bruised, I gave up trying to pry the tabs to drop the block to replace the 140, and I soldered it.
Live to fight another day...
I'd like to thank the OP, Antman, and everyone who contributed to this. I blew the 140 installing the big 3 when the cable slipped and grounded to the engine -POP! Lesson learned - remove the battery.
I'll admit, I failed miserably! After 2 days, about 7hrs in all, and with a storm brewing, my hands and fingers sore and cut up, my back aching, and my ego bruised, I gave up trying to pry the tabs to drop the block to replace the 140, and I soldered it.
Live to fight another day...
Paragon1
Member
How'd you go about soldering the fuse?
Last edited:
ElectroBoy
Banned
Greetings, Rig.
I’ve read lots of your posts in various threads and enjoyed your insight and knowledge of modifications and the troubleshooting help you provide. Lately I’ve been reading about the “Big Three mod” in threads in this and in other forums, and in car stereo installation sites.
As you’ve discovered and have written about, proper fusing of electrical systems can be complex. Especially when considering multiple fuse paths are in a circuit. And selecting fuse type, size, derating them for temperature, and considering the effects when a fuse blows and if the current can take another path. Like in the case of the alternator output to battery positive fused connection.
Before I install this Big Three mod I’m trying to figure out this fusing dilemma. If you fuse per your original Toyota safety plan, with the fuse on the fender wall, you pointed out the problem of a long wire being vulnerable to damage. Later you modified the design to a circuit breaker closer to the engine fuse box, less susceptible to damage. Then you realized a blow of the parallel fuse (breaker) circuit would shunt the increased current to the OEM 140 Amp fuse and blow it, which is a PIA to replace.
With your latest design you have a direct wire connection between the alternator output to the battery, alleviating the cascading fuse blow scenario. But now this has me worried. From what I can tell from research, the primary reason for a large value fuse in that lead is to protect the battery from a short to chassis GND. One failure mode possibility is a short on the load side of the battery, and another is a short in the charging side, that is, the wire at the alternator breaks loose in a collision, or if there is an actual short in the alternator itself.
Although this alternator side short has a low probability of happening, it is a catastrophic event for the battery and now there is no fuse protection in this wire path.
Am I thinking of this correctly?
What are your thoughts on this?
chilipeppermaniac
New member
So it happened. All the leaves were brown and the sky was gray. And while installing my power tray with the fuse box cover off I shorted the line that feeds the alternator into the fuse box and ended up blowing the 140A alternator fuse.
Now since I was in no mood to fix the issue right away I jammed a nut temporarily so I could drive around... and let's just say DONT do this. The moment you put any significant load while driving you'll 4Runner will start reeking of Japanese hooker bots set to 11. What's even worse is the smell since somehow the fuse box is seems to have a direct line into the HVAC system.
So after pondering whether to do the bypass, goto the dealer, or DIY I ended up with the DIY. Reason being is I didn't like how the bypass would look poking out of the fuse box nor did I think the dealer would take care of my rig with all the electrical stuff I have.
Over all the whole effort took 1 hour and was relatively easy. Since easy is a relative term I can pretty much guarantee that if you lived your pre-adolescence days without one of these in you Lego set you'll be just fine.
Now onto the removal. First you'll need to remove this relay box by inserting a tooth pick to release the tab followed up by lifting the box up. Once removing it you'll see a few tabs that lock the lower fuse box to upper fuse box.
Since the fuse box was clearly designed by the Indian god Vishnu and poor old soul like me doesn't have the luxury of having 4 arms - there was a need to figure out how to unlock the tabs that lock the upper and lower fuse boxes together. What I found out to work the best without damaging the box was tooth picks. You'll need to find every tab to unlock (they're all around the fuse box) and insert a tooth pick to unlock them. There are also a few tiny tabs that you can use a flathead screwdriver while you are working apart the lower and upper fuseboxes.
Tips:
-I found it easiest to work apart the fuse box from the side closest to the engine with it anchored down with at least one screw
-There's a zip tie holding the positive wire from the battery into the fuse box. Clip this off as it'll give you a lot more room to move the box.
-Near the fender you'll find a wiring harness on the protruding from two sides of the fuse box that are then anchored down to the body with plastic clamps. You can undo these clamps to give you more room.
-On the same wiring harness you will need to remove the electrical tape as the tape actually also holds the two halves of the fuse box together.
Once you get the two halves separated you get to see this! Since I didn't find much on the internet on where to go from here I'll save you time by saying there's NO WAY you'll be able to remove the alternator fuse from here. Right at this point you're about 60% done but the rest is much easier.
The pics above will show the location of the fuse block tabs. I found it best jam a bunch of 3/16" flat head screw drivers in while pushing down on the fuse block till it looks like the last picture. Just note that this part requires quite a bit of force because you're working against all the wiring behind it.
Once you have the block popped out you'll be able to see the bolts holding the fuse in. Carefully remove them on each side and replace the fuse! The rest is pretty much a reversal which is real easy. Just be extra careful when joining the top and bottom fuse boxes back together as the tabs sometimes do not line up too well.
Thanks for this. I am and was part way through this disassembly because I blew this dumbazz fuse too, along with a few other small ones when I stupidly reversed the leads on my jumper pack to the battery terminals. Trying to jump start a battery that should not have been dead simply from a few years low low usage.
I learned the methods of separating the upper and lower halves of the BOX, but struggle to get the internal clusters of fuses lowered so I can access the bolt screws holding the fuse in. FYI, I have cursed the engineers and Japanese car builder for such a stupid design, each of the half dozen trips I have made to chip away at disassembly of this dumb fuse box design.
WHY is every other fuse a simple unplug affair, while this bastard has to be bolted from inside the most frustrating to pull apart nightmare of an enclosure? This makes the easily breakable brittle Ford plastic wiring connectors look like genius works of art, compared to Toyota's cluster Freak.
Now I will try the zillion screwdriver trick on the cluster that houses the 140 A fuse to see if I can push it down and finally out far enough to remove the screws and fuse so I can install a new one.
To be Cont.
chilipeppermaniac
New member
Cont.
SO far I still struggle to get the fuse blocks lowered out of the larger fuse box with all the dumb tabs I must release and not being an octopus.
However, I did order a pair of the 140 A stupid bolt in fuses, and a small batch of Bussman 7.5, 10, 20, 30A Mini fuses to replace the few I also blew.
SO far I still struggle to get the fuse blocks lowered out of the larger fuse box with all the dumb tabs I must release and not being an octopus.
However, I did order a pair of the 140 A stupid bolt in fuses, and a small batch of Bussman 7.5, 10, 20, 30A Mini fuses to replace the few I also blew.
nofriction
New member
Same Situation!!!!
As with everyone else I'm still struggling with the tabs! Any suggestions for removing the connection from the positive terminal where it connects to the left of the fuse box? I've unbolted it and it appears it should slide upwards, there appear to be 2 tabs, one on either side, but no amount of fiddling seem to release them - any ideas? Thanks!
As with everyone else I'm still struggling with the tabs! Any suggestions for removing the connection from the positive terminal where it connects to the left of the fuse box? I've unbolted it and it appears it should slide upwards, there appear to be 2 tabs, one on either side, but no amount of fiddling seem to release them - any ideas? Thanks!
140 amp fuse
There is now some good information on YouTube on how to properly (and improperly!) replace this 140 amp alternator fuse. I will post a few photos when I qualify to post. This job took me a few hours including time to research the process and then stumble around learning about Toyota's lock tab systems. I think the pros can do the proper repair in a few minutes. The question is, why did the fuse open?
There is now some good information on YouTube on how to properly (and improperly!) replace this 140 amp alternator fuse. I will post a few photos when I qualify to post. This job took me a few hours including time to research the process and then stumble around learning about Toyota's lock tab systems. I think the pros can do the proper repair in a few minutes. The question is, why did the fuse open?
Hammerklavier
Junior Member
I signed up just to add to this thread because it was such a great help to me.
Each step of disassembling the fuse box took me about 3 hours to complete for a total of 6 hours.
The toothpick method was difficult (as expected) but fairly straightforward by following this thread and videos on YouTube by Mammoth 4Runner, Ironhorse Overland, and Vixen_Genie.
The videos were very useful; however, they all cut to the final result without showing the actual struggle of getting these pieces apart!
The second step, popping the plastic piece out of the upper half, which people in this thread have expressed frustration with, was darn near impossible. I didn't have 5 flathead screwdrivers of the appropriate size to employ the method in this thread.
My solution? Just shove that screwdriver as hard as you can into those slots until the plastic bends, and break the darn tabs. The box snaps snugly back into place when reassembled so who cares. Then turn the screwdriver over (or use any available blunt instrument) and push as hard as you can on the edges of the plastic, and directly on the blown 140A fuse, to shimmy it out of place.
Once the bolts are out, the wires are stiff and finger room is limited, so a small telescoping magnet really helps for lining them up to get them back in. (And retrieving when you inevitably drop one!)
Each step of disassembling the fuse box took me about 3 hours to complete for a total of 6 hours.
The toothpick method was difficult (as expected) but fairly straightforward by following this thread and videos on YouTube by Mammoth 4Runner, Ironhorse Overland, and Vixen_Genie.
The videos were very useful; however, they all cut to the final result without showing the actual struggle of getting these pieces apart!
The second step, popping the plastic piece out of the upper half, which people in this thread have expressed frustration with, was darn near impossible. I didn't have 5 flathead screwdrivers of the appropriate size to employ the method in this thread.
My solution? Just shove that screwdriver as hard as you can into those slots until the plastic bends, and break the darn tabs. The box snaps snugly back into place when reassembled so who cares. Then turn the screwdriver over (or use any available blunt instrument) and push as hard as you can on the edges of the plastic, and directly on the blown 140A fuse, to shimmy it out of place.
Once the bolts are out, the wires are stiff and finger room is limited, so a small telescoping magnet really helps for lining them up to get them back in. (And retrieving when you inevitably drop one!)
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