Why are harness grounds the way they are?

[turbomacncheese]

Well, I took a slight detour. Summer AZ heat is NO joke so I got into some 3d printing and cnc routing. Next thing you know, I have to build a laser etcher, upgrade the router, and make a crapload of stuff for wifey to sell at craft shows.
Anyway, back to work on the wires. I think I only have a dozen or so more circuits to finish before moving on to the ground circuit.

My plan is to rebuild it just like in the diagram, so nobody yell at me about how dangerous it is to go off-script. But I wonder why things are grouped the way they are. They pretty much all go to the chassis, directly or indirectly. Aren't the fuses "in front" of the loads in the circuit? So as long as the ground is THERE, what does the grouping affect? Is it a matter of convenience? Just keeping the wire size down to save $$? I'd be happy with a link to a video or page if it's a pain to explain, but I haven't found any yet.

Thanks

[STiPWRD]

I'm not an electrical engineer but my guess would be to reduce the voltage drop. If there was only one ground, the longer wires would have a larger voltage drop than wires close to the ground. This can impact sensors and circuits that need a minimum voltage to work properly. Also for redundancy - if one ground degrades, there are other grounds that can pick up the slack. There may also be a reason related to timing and keeping all the ignition/fuel pulses synchronized. Just some of my theories...

[Bob_n_Cincy]

I will try and explain in layman terms "why the harness grounding are they way they are.
To make it simple, I will just use 2 components. A fuel injector and a throttle position sensor.

All my voltage readings are reletive to the negative post.
The battery positive post is 12.00 volts.
When the fuel injector is off, both of it's wires on the injector are at zero volts.
When the fuel injector is on, there is current flowing through both the ground wire and the trigger wire. So the ground wire at the injector might be at 0.5 volts and the trigger wire might be at 11.5 volts. This is caused by resistance in the wiring.

Now lets talk about the throttle position sensor. When throttle is at 50% the ground wire is at 0.0 volts., the supply wire is at 5 volts and the sensor wire is at 2.5 volts. so it is working properlly.

Now if we share the ground wire on the fuel injector and the throttle position sensor. When injector is on the ground for each device goes up to 0.5 volts. so now the the throttle position sensor wire is at 2.75 volts. This is the 50 percent point between 0.5 volts and 5 volts) So the ECU gets bad information.

I hope you see here with dozens of device the design and layout of the ground system is very important.
Bob

[turbomacncheese]

Awesome. I think I remember that there is a voltage drop after loads in a circuit, but don't think I ever considered that it isn't required to be a "one-way street" back to the battery. Of course, I never got more electrical theory exposure than in HS intro to physics.

Also easy for me to forget that just because the battery is 12 volts doesn't mean everything else is 12 volts.

Thanks for the clear example. Great way to start my day!