2011 jeep liberty big three wire upgrade

Yes... but: Firstly, I understood the big 3 to include the alt-battery +12V, but apparently not so. I guess my 'big 3' therefore is 'the big 4'. Definitely the +12V alt to battery needs an upgrade for upgraded alternators, but it may well be worthwhile for OEM setups. Then again, the alt to batt voltage drop is not that important power-wise IF the alternator is monitoring the battery. Hence for single wire alternators (D+ or L (charge-Light) only types) where the alternator can only monitor its output +12V, a low alt-batt voltage drop is important.    WRT ground wiring, I consider batt- to chassis, batt- to engine, & engine to chassis to be equivalent noting that TWO of those are required, but the 3rd can be added to further reduce voltage drops or provide redundancy (ie, only 2 are required so 1 of 3 can break). Some vehicles split the batt- to engine and chassis respectively. (Most old vehicles did as does your Jeep.)   But others may use batt- to engine, and engine to chassis. The key 'heavy' GND in any vehicle is the batt- to startermotor GND (ie, engine) assuming they have electric starters. Since traditional startermotors are usually 200A or more, that x00A capable starter/engine to battery- GND has no problems carrying typical alternator currents - tho I have seen small GND cables used which IMO are NOT suited for continuous cranking (ie, that GND will get warm/hot) but should be fine for OEM alternator outputs). Tho in my vehicles I'd typically add an engine-chassis GND to its OEM batt- to engine & chassis GND, my current vehicle has a heavy engine to chassis GND and a heavy batt- to engine. (The latter coincidentally using a startermotor mounting bolt after deciding NOT to use a common bolt for both batt- & chassis GNDs after a problem a few years ago). In part the batt- to engine to chassis is because it may be difficult having TWO heavy cables to the battery -ve terminal. But I also have some load GNDs direct to the batt- eg, audio, 2nd/aux battery(s), electronic accessories (GPS, phone, PC, cameras, etc). Not that my audio is big - a typical HU with 10A fuse - nor that the others are big (except aux battery charging), but the principle is the same for big loads. Plus I probably have a smallish batt- to chassis connection... But the above - and what may be the best wiring - can depend on desires & application. And many may use a compromise point as the main supply (+12V or GND) for various reasons. EG - the +12V junction or fusebox where both alt +12V and batt +12V meet. (Startermotor +12V is (almost?) always NOT included in that junction.) But I'll address that along with alternator bolt grounding in my next reply.

There's really no sense in trying to figure out the "direction of flow"- and in fact, there are opposing theories about it, depending on who you ask. Suffice it to say- both sides of the circuit need to be upgraded. The end."Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"

Ok, compromise points, where to GND, etc. Geez, where to start...?? Maybe first a little anecdote. Ok, you got me - maybe first an little anecdote. I recall discussions of "ABSOLUTE ground". I often find them amusing because they fail to state the conditions - ie, when the alternator supplies the load or when the battery supplies - eg, at idle, under high total loading, load transients, or when not charging?   (So MANY web opposing arguments I see are a waste of existence - both or many are correct (or rather, not incorrect) - they simply miss defining the conditions!) I recall one audio system example where the big deal seemed to be how the alternator supplied the most -ve voltage and hence was 'the absolute GND' and therefore the alternator case/bolt was used as the GND. In my experience that is problematic and unnecessary except for certain rare situations... But there I was thinking (apart from the various electrical considerations!) how do you securely mount BIG audio GNDs to an alternator case or mounting bolt... which in turn is on a hot and vibrating engine? A 0/2G or 00G cable flying across to the engine to an eyelet to a (smallish?) mounting bolt, or bolted into an alloy alternator case...?    Then it turned out the audio system involved was a mere 100W or similar! Now if their added wiring couldn't handle 10 or a few tens of Amps without significant voltage drop... Now if being that pedantic, IMO the alternator case might not be the 'absolute' GND anyhow. But forgetting that and the other issues, they obviously didn't care about DC supply noise nor the GND that is used during amplifier burps (surges) etc (like I said, it was a small system...). Nor if chassis or batt- grounded accessories connected to such an HU or amp or PC there could be GND path issues and hence noise and maybe even damage. BTW - for my discussions, chassis & body (and dash grounds etc) are equivalent. It is assumed that they are one & the same electrically - ie they have adequate & good condition interconnection if they are separate mechanical items. Anyhow, the above was an example of arguments I have oft heard & LOL'd. Without sufficient details or conditions a correct answer cannot be assigned. But I'll tackle if from a ground up POV. (That ground up pun is simply natural!) First and foremost is physical (or economic) practicality. A heavy gauge audio power cable mounted the engine or alternator bracket? It's bad enough having a fat cable attached to the alternator output - it gets hot and vibrates hence might fatigue, anneal, suffer insulation breakdown, etc - but to double up on that by attaching a GND to the (probably hotter) alternator mounting bolts or engine block... Likewise multiple heavy cables attached to battery terminals? Even with suitable terminals, will it strain the battery housing or mean longer paths or be too messy? (Batteries are usually mounted to the front of the engine bay. Main fuseboxes or may be closer to loads than the bat or alternator, etc.) Then there's the electrical aspect. If the alternator can't supply the load, the battery supplies the GND & +12V - ie, the batt- is the most -ve. That occurs when the alternator falls short - eg, transients, overloads, engine off. Sure, normally the alternator supplies the voltage (hence its GND is the most -ve), but then we get into the issue of running cables to the engineblock or alternator. What is usually done in practice is chassis-based 'power' points. Relay- or fuse-boxes else special insulated studs are used to be a junction of the alt output and batt+ to supply +12V to everything else. (Startermotors, winches, big audio/loads excluded.) Similarly batt- and alt/engine GND join at some chassis point. Those common or 'central' points are often closer to the loads than batt+ or batt- or alternator/engine and they have the advantage of fixed solid chassis mounting which is probably cooler and vibrates less than engine mounting. (Hence no need for multiple very multi-stranded and heat tolerant cables to the engine.) IMO if any the above suffer voltage drops, upgrade the applicable cable or connections. Ideally all points wired together are the same electrical point but that ignores cable & joint resistance. Hence why we minimise cable resistance and temperature - eg, use copper instead of Al, steel, or gold; appropriate purity, stranding and annealing etc; and use appropriate interconnection techniques. From Ohm's Law, every conducting wire has a voltage drop - V=IR. (Let's ignore superconductors.) The higher the current, the bigger the voltage drop. If it's too high, we need to reduce the resistance (eg, bigger cable, shorter cable, better conductors, better joints, lower temperature). Usually cable size is increased (since we assume we already have the shortest paths and good connections), and often merely by doubling up - eg, another parallel cable of the same assuming that's practical. I think there's enough above to enable you to decide, but maybe a few clarifications or examples... Audio and PCs etc often use the battery as their power source because it's the cleanest DC power (a battery acts like a cap and smooths out much electrical variation/noise). That may include the batt- for GND if the main or central GND is inadequate. Big audio often uses the battery because it's the most likely to provide for burps (a battery is like a huge capacitor). Even if an alternator can handle a burp or surge, the battery might be faster reacting. That's certainly true for older mechanical voltage regulators but with modern electronic all in one alternators with regulators it depends on so many factors. Suffice to say, when the load or transient magnitude exceeds alternator capability, it will be the battery that (eventually?) supplies the load. Another old example which is irrelevant to modern LED & HID headlights etc... I used to power my halogen lights from the alternator output for max light output when driving. That could make considerable difference - and extra 0.5V makes a big difference with halogens, far more than with tungstens). But now they are direct off the battery because (1) I use heavy wiring too inconvenient to mount at the alternator output; (2) alternator vibration etc & inconvenience; (3) my alt to batt+ wiring voltage drop should be negligible anyway; (4) my battery is usually 14.2V else 14.4V anyhow (it used to be 13.8V in ye olde days). There are issues I haven't covered - especially transient and sub-transient response of alternators... and batteries; source (battery) resistance or impedances; the non-capacitive power desirability of high peak SPL competitive setups etc - but it's merely a generic discussion and not any specific solutions. And I'll avoid alternator fusing. Just note that if used, the fuse should be at the batt+ end (the fuse is not to protect the alternator).

PS - Direction of flow is irrelevant. The flow is in both directions anyhow. (There are no opposing theories, it's just that people that say it flows one way have not defined the situation. Geez - where have I heard that before?)    It's like fuses - they are not placed on the +ve side because conventional current flows +ve to -ve, but because +ve is the hot side on -ve earth/ground vehicles. (Look at AC 'active' fusing - the 2 generator outputs are equivalent until one is referenced to earth/ground or whatever ref point. NB - or its 3 phases or 4 outputs for 3-phase systems.)

Oh man, definitely a lot of good information there. Thanks a lot for taking the time to post it all. There's a lot to think about now, especially sitting around waiting for a bit of warmer weather haha. Guess we'll see how this goes!

Thanks for the thanks. Sorry if it is too much info. Others often prefer less up front info so they can learn a bit at a time (ie, from mistakes, or replace the "now insufficient" install they just did). IMO the basics are simple... You can never have too much grounding. [ IE - it's better having too fat or extra grounds, especially when loss of GND can cause HEAPs of damage (eg, engine GND loss can fry throttle & speedo cables, thin wired GNDs, engine electronics; body GNDs can fry electronics). ] One exception is if it creates ground loops (noise) but that should never involved the 'heavy' big-3 GNDs.    Similarly you can never go 'too big' on hot (+12V) wiring. [ But GND should/must match if not exceed hot wiring capability. And very oversized cabling etc may be uneconomical for the gain involved, etc. ] Of course all (power) sources must be fused. [ For distribution, that is to protect the downstream cabling, relays, etc until a smaller fuse takes over. And there is nothing wrong with having 200A distribution for a 10A circuit (which might be fused at 10A or 15A etc). Equipment fusing is usually internal to the equipment else (usually) at the equipment end. ] The rest are usually individual design preferences... If adding to existing power circuits, are they clean enough or switched appropriately and have the required spare capacity? Or... Do you want power straight from the battery (cleaner DC) and hence use a relay, or use a relay so you can easily provide reverse polarity protection or combine various input triggers [ eg, manual switch, amp remotes, engine signals - ie, easier to combine signals thru low power diodes or electronic logic than combine heavy power feeds)? ] Get GND from body/chassis or more directly? [ eg, from battery -ve terminal or engine/battery/chassis GND point? ] Do you allow for future expansion or additions? Maybe that summary is still too much? If so, ignore the [bracketed detail].

Alright so from what you've posted, I think I decided what I'm going to do. Where the factory ground strap runs to the engine block is basically inaccessible - there is no way I'm getting a socket down there to run additional wire. My plan is to run 4 gauge wires between the 1) alternator + and battery + (fused of course) 2) alternator bolt bracket (alternator case/ground) to battery - 3) two runs of 4 gauge from battery - to chassis With the amps grounded to the rear seat brackets, which are welded to the chassis, I don't see any reason why the firewall ground to engine block ground would matter considering I WILL upgrade the chassis to battery - which then runs to alternator ground.

That sounds ok. I'd be surprised if you couldn't find some gearbox to chassis point, but that may not matter. I should have mentioned how NOT touching the OEM grounding has a big advantage for new vehicles - namely that it cannot effect any warranty. Hence the usual advice is to ADD straps elsewhere. And that's what you are doing.

You won't need to carry a ground wire back if you measure the resistance between a local ground point at the rear and the battery NEG terminal. 2ohms or less will be fine and save you a possible RF induced interference loop.Test before boxing up.

2 Ohms, or 2 milli-Ohms? 2 Ohms @ 1A is a 1V drop. 2mR @ 100A is a 20mV drop. But it is difficult measuring mR (m-Ohms).