Originally Posted by 98OzarksRunner

... The safe way to do this is to remove (or disconnect) the wire from the fuse box to the alternator (wire #3 in the diagram) so there is only one fused path between the battery and the alternator (leave the fused link connected to the battery).

Originally Posted by IBallEngineer

Let me start by saying I think the big 3 is big to do about almost nothing. I haven't done it to mine, nor do I intend to. 175K and no indication I will need it. Still I see the benefits IF, there is an alternator upgrade, or additional batteries, or you have not maintained the terminals/wires. So now to the problem.

Too many assumptions here. First the resistance in the two branches is NOT the same, that's the whole purpose of the upgrade. 2nd, if there would be a short to ground drawing big amperage, it would happen in an individual branch of the circuit. Since the current would take the path of least resistance, one branch fuse WOULD blow, most likely the added circuit breaker because that would be the path of least resistance. Of course you'd still have voltage, and therefore current flow because the 2nd branch would still be live. I haven't tested this, but I do think the 2nd fuse would then blow.

Now, if the alternator itself caused the short it would most likely draw all the battery could give, in which case 240A is nothing. Hell the starter could draw that much. Of course by design a short circuit anywhere in either branch would be just as catastrophic in terms of amperage draw.

And THAT is why this is really NOT a safety issue at all. Unless someone tells me that people doing the big 3 are burning their rigs to the ground.

That being said I agree with Ozark dude in that bypassing the original alternator circuit would be prudent. The redundancy is unnecessary anyway, and who wants to have to deal with a blown factory 120a fuse. Let the breaker do it's job and move on.

Originally Posted by Dezerts10

lots to read here when I go to move my battery and add a secondary battery behind the rear seat.

But quick question... my negative to chassis wire has been disconnected for ever. previous owner had the wrong size battery in place and battery moved a lot when off roading and broke that cable. Ive never re connected it because I haven't really known what it was for.

Also when I relocate the batteries, can I run a cable from the negative to the frame to accomplish the same thing?

Originally Posted by RAD4Runner

Sorry to rain on your parade, guys but, I second the posts below by 98Ozarks and iballengineer.

My ten cents:
Stock circuit is already well-designed. Issues arise from bad connections, poor maintenance, etc. A better upgrade would be to inspect, clean and tighten all connections. ALL, not just the cliched "check grounds", THEN to run all after-market from a separate fuse-block connected to the battery.

If you still want to upsize your GROUND wires "4" & "5" (say, because you plan to use body ground as return path for added circuits), go ahead but paralleling 2 Fuses is not recommended (new wire 8 bypassing main fuse), as discussed by IBallEngineer. A better way is described by 98Ozarks4runner:


In other words:
1) Remove wire "3", and design Wire 8 and circuit breaker for desired TOTAL capacity (240A?). This way, batt and alt output are working directly hand-in-hand, like on GM system.
2) Remove and replace "4" and "5" with desired thicker wires. No need for "6". Ideal grounding ALL leads DIRECTLY to battery negative, not through a loop like 4-5-6.
3) Power all auxiliary circuits from a fuse box/ CB directly connected to battery. IF anything goes wrong with auxiliary circuits only the aux fuses blow, stock circuits keep on working and you still get to destination and home.

Originally Posted by Toyojay

I feel like this makes sense, having two 120A paths for electricity to flow doesn't seem safe, while it was designed to have one. While electricity will take the path of least resistance, and it does make sense that it will travel the added circuit first, blow that fuse and then move to the factory #3 wire and hopefully blow that fuse killing all the power, right? In theory it should work that way if I understand this right. I'm just not sure if the small gains are worth possibly damaging the ECU, main harness, fire...etc.

Originally Posted by rideexileex

As an EE, and with a stock alternator, I feel that the only beneficial wire mod is the 7 for a better battery ground. Everything else is going to only net marginal gains that don’t justify the cost and time involved. I bought a pre-made ground cable at Napa for ~10 bucks and I’m done.

Originally Posted by rideexileex

As an EE, and with a stock alternator, I feel that the only beneficial wire mod is the 7 for a better battery ground. Everything else is going to only net marginal gains that don’t justify the cost and time involved. I bought a pre-made ground cable at Napa for ~10 bucks and I’m done.