How do you know if a ground connection is right? And how to properly branch circuits?

It is still ground.

The term ground can have different meanings. In residential or commercial terms it means zero potential, actually connected to earth. In other applications it can be just a point of reference, it might actually have a voltage on it.

 

Exactly. Another way to think about a vehicle "negative ground" DC electric system is that the positive (+) is one half and the negative (-) is the other, equal, half of the same circuit. For electricly important circuits, each half should be treated the same. The term "negative ground" just means that the negative side of the circuit happens to be attached to the chassis. Often accesories can be powered by running the negative side to the chassis. You can call it a ground but is not the same as thing as a ground in a 120VAC circuit. As s4nsc said, in a 120VAC circuit that's not malfunctioning and is wired correctly, the ground should have no potential. In a vehicle 12vDC circuit the "ground" is part of the working circuit.

 

Rule of thumb from the car audio world.

1. If running an independent ground, match the size of your power lead assuming that is appropriately sized and fused.

2. If using bus bars/joining grounds, insure the ground wire is appropriately sized for the sum of all power sources/circuits.

I always include a margin of error because length of the wire influences max power per wire size to some degree.

 

The concept of ground being a point of zero potential is correct, but in a vehicle that is inherently ungrounded it’s actually just a reference point. Your house is tied to earth ground unlike your vehicle which sits on four rubber insulators.

Any “ground” is intended to be a non-current carrying conductor. At your house, the white (neutral) is at the same potential as the bare ground conductor, but the neutral is sized to carry current...unlike the ground conductor.

Don’t mistake the purpose of a ground and the negative (black) conductor in your vehicle. They should be at the same reference potential, but the ground conductor is a means of bonding parts of the vehicle together, and the black negative conductor is part of a current-carrying circuit.

Often these bonded components are (mis)used as the return path for the negative side of vehicle circuits, but for higher current applications always run a dedicated negative sized the same as the positive (red) conductor.

 

Don't know if it helps clear it up, but old school way of checking for a "ground", or positive getting into the ground or negative side is to take an old 12v bulb from the tail light and put one of the contact nubs on its base to the negative post of the battery with the negative cable removed and put the removed cable on the other contact nub, using the filament in the bulb to complete the circuit. If all is good, nothing happens. If the bulbs filament glows you have a short somewhere and somehow the positive is getting to the chassis. Same as using a meter but old school and works better in a dark area, obviously. Thanks to my brother for teaching me that one.

 

So I didn’t have enough wire to run the negative back to the battery. Just to see what would happen, I ran the negative from the fuse box to the rack.

With this configuration, I’m loosing .4 volts between battery and fuse box.

Curious to hear what others think about this.

I will insulate the rack around the fuse box.

 

I know I am behind on your threads...
But I assume the 0.4V is with fridge running.

Seems high with what size wire you are using.

Have you isolated where the voltage drop is showing up?
(Hook a wire from an extension cord or similar, to the battery negative. Hook other end of the extension cord to voltmeter negative. Check positive on voltmeter to each location on the circuit with fridge running. IE battery, panel power, fridge power, panel ground, fridge ground, frame, battery...)

 

Yes, with the fridge running.

Ok. I’ll do this tomorrow. Solo with the kiddo tonight.

 

I was interrupted yesterday and forgot to switch off the fridge. Drained the battery down to 1.6 volts. Hope I didn’t damage it.

It’s on the charger now. It’s an older charger but I’ve got it on the lower 2A setting. Going to get it charged up a bit then jump it and go for a long drive...

 

With checking voltage drop you can move the test leads to different points to narrow down where the high resistance is. I'd check all the connections with the circuit under load and see where the majority of the drop is.

 

To clear things up a bit, I have a 6 circuit blue sea box w neg bus in the engine compartment. I realize the wiring is sloppy here and I’m going to tidy it up once I figure out what my next step will be.



Then, I temporarily have the 6awg wire coming from a circuit on this panel going to the same type of fuse box mounted on the rack (bed location).



So after tightening things down again, and removing the fuse from the fridge circuit at the panel mounted to the rack, I’m getting .00 drop at all points, from battery to fuse slot at panel installed on the rack.

When I replace the fuse, and with the thermostat on the lowest setting, there is .15 drop at the battery, and .24 drop after the first fuse (panel under hood).

Then hooking up the extension cord to the neg batt post with a clip lead, there is .17 drop between batt pos and neg at the other end of extension cord.

.35 drop between pos terminal (where the pos comes into the panel) on rack fuse box, and .42 drop after the fuse on that same panel.

Without load, there is .00 drop when measured between pos on rack mounted fuse box and the frame. With load, there .24 drop.

It occurs to me that I should probably repeat all of this with the engine running to maintain the battery’s charge.

 

The combination of these 3 on one fuse would mean a circuit capable of running a 15 AMP fuse :
50w 2 meter / 70cm
25w 10 meter
40w 10/11 meter
+
115 watts which is right around 10 amps. This on all at the same time would be too close for a 10 amp circuit wired for 10 amps and fused at 10 10 amps . It seems you have found a wire gauge to watts / amps chart. If not google for one or ask .

IMO Mtn Mike is giving you the best info and I would say he has wired things like boats with no frame to ground in the first place, or has wired motorcycles with plastics everywhere and so everything needs a individual ground wire . Bold happens

I am not familiar yet with the composite bed on my 3rd gen taco to know where to grab ground easiest.

 

Had to make a sketch, this look right?

Next step (for me to be able to help any) will be to figure out the voltages you are reporting (or voltage drops) via letter, Vg-h, Ve-a, Vc-d etc....
That said, each of those 15amp fuses is using about 0.05 - 0.1 volt each, depending on the exact amperage... so they are definitely adding up.

 

This looks right with the exception of the engine compartment fuse panel which is connected directly to batt negative.