where is the true ground?

It does get tricky.... Even the experienced have different views. Whilst other experienced are just plain wrong (...at times - it happens!). But excluding ground loop issues (and cost & weight), there is little reason NOT to run ground cables as well. The total resistance will be less than that of the cable or metalwork (ie, parallel resistances).    I run a heavy figure-8 cable (ground & +12V) to my 2nd rear-mounted battery. But that battery is not body/tray/chassis connected. But no harm if I were to - assuming a good path, else never breaking the cable ground return!. FYI - it's merely a spare battery - used for occasional fridges, or if my main battery flattens. I also run similar but smaller to my Alpine (which may only be 16W x 4, not the whopping 45W x 4 that I thought it was!), but that's more for noise (dedicated +12V from battery) and wiring simplicity. But it normally has its chassis grounded to my body/chassis too (just not for the last year or 3?). But the biggest voltage difference (between gnd & +12V) is either across the alternator (B+ & its chassis) else - when the battery is supplying - across the battery terminals. Anywhere downstream from those points has to be a lower voltage - even if the drop is negligible. (If it isn't get, a better or true-RMS voltmeter! Else find out why your wiring is auto-transforming itself to increase voltage.) For large systems, the only way to minimise the impact of high-current surges is a second battery near(er) the amp etc. I say second because main/primary batteries are usually flooded (wet) and designed for high cranking currents. The 2nd "amp" battery must usually be sealed if mounted internally (boot/trunk etc). And usually it's an AGM (aka Valve-Regulated = VRLA, often aka "Sealed(sic) Lead Acid" = SLA). Gel cells are another alternative (are these NOT SLA batteries?).     Whether the 2nd battery is deep cycle or cranking depends on what you want it for (long running without the engine, or high-output surges) - batteries normally being either one or the other by construction. (Yes - I am familiar with the hype. And the field comments.)    Interestingly, both battery types often have the same quoted ESR, but let's not go there... But to minimise losses & dips, first upgrade your wiring (the big-3 etc); then the alternator if it needs it; maybe more wiring upgrades; and maybe a 2nd battery - AGM of course! (FYI - other than ground loops, cost & weight - I see no harm in "continually" paralleling ground straps and cables. There are usually heaps of possible paths. And unlike hot +12V wiring, no hazards. (The only hazards being if ground straps are insufficient!) But there is a point where the gains become negligible - or the mpg increase outweighs the 0.0000632 uuOhms & 16+ tons of ground strap gains) Although primary batteries can be upgraded, I consider that a waste or compromise compared to a 2nd battery. Even a primary AGM is compromised by cable losses. Better to keep the same standard (cheap?) main/primary battery, and then add whatever sized AGM near the amplifier/subs - whether a small 1.2AH in place of a capacitor, or a larger 40AH, 100AH etc etc. But I am assuming non-parallel batteries (which IMO should not be done - despite claims otherwise...) and something akin to my oft suggested charge-light actuated (or voltage sensing) relay that only interconnects the main & 2nd batteries whilst charging. Hence no issue issues with different batteries, and you should have at least one reasonably charged battery for cranking... Ooops, back to earth.... I ran away with the grounding issue - absolutely!

oldspark wrote: (FYI - other than ground loops, cost & weight - I see no harm in "continually" paralleling ground straps and cables. There are usually heaps of possible paths. And unlike hot +12V wiring, no hazards. (The only hazards being if ground straps are insufficient!) But there is a point where the gains become negligible - or the mpg increase outweighs the 0.0000632 uuOhms & 16+ tons of ground strap gains)

There's a lot of good information in that post relavent to a number of threads.

Regarding the quote. Vehicle manufacturers do not design electrical systems with consumer upgrades in mind, they do the absolute least and cost effective thing to get that vehicle on a sales parking lot.

My Pathfinder isnt the first system I've seen where I'm almost astonished it keeps running after 5 years based on the chincy materials and workmanship in the electrical dept.

On this vehicle, I used a dremmel and cleaned the existing contact surfaces, and added more clean bare surface area where ground distribution existed. I also added additional cables.

My current application (no pun intended) is different, I just want to provide the best possible high current both front and back for my winch, which can suck 300+ amps depending on load. And do this, in a manner that doesnt jeapordies existing circuitry.

*there are Nissan KB articles about where to ground to avoid fault codes*

I totally agree that adding some additional grounding and cleaning up is worth every penny, about to and about $20 and an hours labor.

anonymous1 wrote: Vehicle manufacturers do not design electrical systems with consumer upgrades in mind

You are correct. But elsewhere someone said something similar regarding alternators and their capacity, and I thought that was misleading. They were suggesting that the alternator was NOT designed nor capable of handling extra loads - in this case low power entertainment stuff (meaning 100W-200W of carPuter etc, not BIG audio). I thought how common it is - or was - to add driving lights without experiencing problems. EG - add 2x100W lights and the system would handle it fine - the battery would not flatten over time etc. Anon's context however is different and refers to the provision of cabling as well. Yes - they keep it light & cheap. They include cig sockets. Some recreational vehicles may include rear power plugs (cig sockets or other). Hence they allow for some consumer upgrades - like GPS, mobiles(cells), chargers etc. But when it comes to big consumer upgrades, it is taken for granted that consumer supplies the required heavy battery terminals, wiring, and distribution. And so many forget the grounds! (Was it in 12volt ~12 months ago that some Hummer or similar lost ~7-12 DVDs/screens and $thousands of dollars of equipment due to high voltage? I'm betting it was a ground break...) All manufacturers have to provide is "sufficient" wiring and grounding so that their equipment functions. Hence a 1V ground drop may be acceptable. But there is no harm lowing ground drops. Double the existing 1V drop cabling to halve it to 1/2V. Quadruple it for 1/4V. Etc. And I recommend the12volt's "Big 3" method - do NOT replace standard ground straps - ADD to them - thereby negating "faulty modification" claims under warranty etc.