LOL true enough. Sorry for the delayed reply, as you've put some solid info together here. I think I ran out of motivation on my own effort (moved away from wiring to trying to get the motor in) which was what was pushing me to ask more questions. I think we're fairly close with what we have though. I'm going to put some more thought into this and likely ask some more questions, including a possible deviation from your above example setup for cars without rear batteries.

 

The Wiring can basically stay the same with a Battery in the Engine-Compartment.
Less or No Fire-Wall Pass Through connections would be needed.

Making a Diagram with the Battery installed in the rear of the Vehicle, just leaves more room to show the layout of the Wires.
But the same layout basically is still used with the battery under the Hood.

 

I figured as much. Only thing that would even be worth considering is downsizing the wire gauge as they're a good bit shorter and may not require being quite so big. However, there's no harm in it so probably best to leave it alone.

 

The Wire size can be down-sized.


I use heavy Gauge Wire to be safe, rather than sorry...
My Personal 3rd-Gen uses so many Electric Components, that I run a 250A Alternator... and need the larger Wire.
I know that many modern Builds also use multiple Electric Fuel-Pumps, Radiator Fans, Cooler Fans, Electric Water Pumps, Distributorless Ignition, Intercooler Water Pumps or Cool-Down Tank Pumps...
as well as Lighting, Exhaust cut-outs, Nitrous Bottle Heaters, and much more!

So there is often the need for the larger Wire... I just make sure my Builds can handle the Amperage demands.

 

I think this thread is ready for the sticky. Folks will surely ask more questions, and I'll probably add some pictures or questions myself as my build progresses. As time goes on, I'll flesh out the couple posts at the beginning with anything pertinent.

Thanks so much @vorteciroc and @QwkTrip .

 

We got lucky as heck with a guy like vorteciroc at the site. It's taken me a while to recognize he's not just smart, he's downright an expert with serious credentials on about anything he speaks to. People should listen when he talks.

 

LOL!

Come on, I thought everyone with multiple Masters Degrees, that went to work as an Engineer for GM...
and then later opened their own GM Specialty Power-Train Systems (Engine, Trans. T-Case, Diffs, PCM, Pow.-Dist.) Shop/ Business...
Were all a bunch of idiots!


All joking aside... There are MANY very intelligent Members here that contribute to the Forum.
So I do not feel that I deserve an more praise than anyone else that contributes.

College Degrees, complex Jobs, and Business success, do not add up to intelligence.
There are also many different forms of intelligence, that can be expressed in many different ways.

So I would like to praise all of you, that are on the Forum.
Thank you for contributing in your own ways, and for sharing the Knowledge/ Intelligence that you posses with all of the Forum.

 

I am still regularly being asked about Clean VS Dirty Power...
and I probably will for the rest of my days... Eesh!

I do not know how much more simply, I can put this.

What you should basically know is:
-Electronics should be Powered and Grounded directly at the Battery (Not a Chassis-Ground, Not a Power distribution Stud).
-Keep Electronics (and the corresponding Wiring) away from High Amperage Devices (and Wiring)...
(Starter-Motor, Alternator, Electric-Fans, Other Electric Motors and Pumps) all need to be separated away from Electronics.

Our Original Third-Gen Wiring/ Power Distribution is arranged so that most everything will receive Power off of the Starter-Motor Stud.
Even in the 1980s with very basic PCMs/ Control Modules...
The Power to the PCM is from the Battery (well almost... a Connector that is from the Battery via Fusible-Link) ...More importantly, NOT the Starter-Motor!

That is about as simple as I can make it.

 

Let's talk about grounding!
Bringing this dormant thread back to life as I've been working on sorting out my wiring harness power/ground setup and in the process of doing so came across information online as well as better knowledge of how my own harness is built that has made me wonder about a few things related to grounding (which as others have said, is probably the most important part of your wiring to get right). You can't have power distribution without a return to the battery!

Some acknowledgements and clarifications.... Big thanks again to @vorteciroc , @QwkTrip , and others in this thread for contributing their depth of knowledge and experience. I'm no expert by any means and frankly am looking to just ensure 1) my car does not catch fire or have serious electrical issues and 2) others that may read this thread in the future know their options, what to do and not do, and if they can make decent wiring connections they too can get their car powered/grounded safely and effectively.

My Particular Setup
I have a Speartech wiring harness from MANY years ago intended for a 411 PCM (99-02 F-body). Overall, I think the general construction on this harness is well done and I've never heard otherwise about their harness. When reviewing how the harness handles grounds, here are my observations:

• ALL grounds for the PCM harness are tied together at a junction point in the main body of the harness.
• There is ground wire that exits the harness and is intended to be attached to the rear of the passenger head with a star ring terminal. The wire gauge for this is either 14 or 16ga, with a nice GM-quality star ring terminal on the end that I'd like to find more of vs. the cheap auto-parts variety.

Evaluating My Harness Ground Setup
Clearly, my harness ground setup is quite different than what was posted quite clearly by vorteciroc above (which I'm going to refer to as the Isolated PCM Ground method or IPCMG). However, it's not that different from what GM utilized from what I've researched either online or via books I've bought. Initial thought on this was that these differences were largely a matter of cost reduction by manufacturers to target what is minimally viable during a warranty period. What GM produced (and other aftermarket companies) definitely works for most people, but there's a difference to understand. I'm after something that 1) works, 2) is safe, and 3) will stand the test of time. Time to start digging.

Star Point Grounding
Most of what I ran across online recommends the "Star Point Grounding" (SPG) approach. This approach has everything in the car tie their grounds together at a common point (the engine block) and AVOID running additional grounds directly from electronics directly to the battery. The quick read on why is that by using this method, the system will work and fail gracefully in the event that key grounding straps/cables corrode or are otherwise disconnected, as well as ensure identical ground voltage levels between engine sensors and the ECU. Here are the most commonly referenced reads/watches on this topic:

• Haltech - ECU Grounding DOs and DONTs (text)
• Haltech - Why is good grounding important (video)
  
  Haltech - Why is good grounding important (video)
• High Performance Academy - Star Point Grounding (video)
  
  High Performance Academy - Star Point Grounding (video)

Comparison and Thinking

1. My harness is currently setup for Star Point Grounding (SPG) and would likely work for my needs, though I am considering either enlarging the ground wire to some degree within the harness or having a second attachment to the engine vs. just one. Some thoughts on SPG method:
   1. I suspect the GM setup for 99-02 F-bodies is also using SPG, as well as many (most?) aftermarket LS harnesses, with many of them functioning for many people and uses. Books on LS wiring harness design and online references confirm this.
   2. In general, avoid duplicate ground connections to the battery & engine from the same device (e.g. PCM). If the ground connection between the engine and battery failed, a large amount of current would pass through the the alternate wire from the engine. This could damage electronics or create a fire hazard. This seems like uncommon knowledge, as many forums online have people creating what seem like ground meshes between engine, battery, body, PCM, etc. etc. in the name of "more is better" without thought to wire resistance due to gauge/length or the electronics attached to those ground circuits.
2. The Isolated PCM Grounding (IPCMG) method posted by @vorteciroc is absolutely sound if followed to a T and certain scenarios are avoided:
   1. Do not add additional connections between the ground circuits (e.g. ground PCM to battery AND something else). If a larger gauge wire failed for some reason (e.g. corrosion), that redundancy would cause smaller gauge wire(s) to carry the load and cause issues either for those electronics or create a fire hazard.
   2. "When done this way, no other circuits should be grounded with a terminal on the Head or Block." vorteciroc pointed this out in post #49. I believe this is particularly true in regard to sensors, but may be more than that. Will need clarification. Related - my harness connections to each fuel injector have both a "low reference" and a ground, whereas others or older applications (pre-LS) may not. Also worth investigating any aftermarket sensors added to a setup (e.g. wideband 02 sensors) to ensure that have both a low reference and a ground. I also do not understand if there are other implications of needing to ground injectors through the engine.
   3. Same as above, but deserves pointing out - avoid usage of sensors which ground through their body to the engine. They must receive a second wire that is a ground back to the ground shared with the PCM.
   4. Any future "fixes" to ground issues must abide by this level of isolation and its importance conveyed to future owners of the vehicle.

I'm very much interested in others' thoughts on this, particularly @vorteciroc (Update: vorteciroc will likely not be replying due to some ongoing health issues, for which we should all think of/pray for he and his family and ensure we spend good time with our own families) or others versed in the theory or sufficient experience. I believe that both methods are sound and likely there are good/better/best forms of SPG as well (which ought to be explored). For me, right now, I think that if someone is unable (perhaps due to lack of knowledge on what sensor may ground to the engine through its body) or unwilling to modify their harness or ground circuit enough to achieve the IPCMG ideal, then it's reasonable to use the SPG pattern and ensure duplicated ground connections are avoided (aka don't mix/match IPCMG and SPG - choose one and stick with it for the life of the vehicle). Doing so, while not "best" is definitely "good enough" for most applications, though your particular application may not fit within that bucket.

I am still considering what forward path is for me and my setup. Things I am reviewing:
- Are all sensors on my harness setup with separated ground and low reference? Or are they tied together anywhere? Answer: all "low reference" wires go back to the appropriate pins on the PCM and do NOT cross with "ground" wires. Double checked this by performing continuity tests on the harness.
- How to best tie together multiple grounds if I were to change to an IPCMG setup - current harness has large solder "blocks" where many wires are tied together