Im currently working out a wiring diagram for my auxiliary fuse/relay box for my truck and I am trying to reduce the number of grounds with in the circuit. I know the factory wiring would take two ground wires and crimp them together into one single wire but I am looking for more information on doing this as I have quite a few ground wires that I want to link together eventually into a single ground wire.

The first bundle of wires would be for my Apollo Driving light and my two H4 hella headlights with a relay powering both circuits. That means I have 4 ground wires between the four lights and what I was thinking of doing is splicing the two grounds from the driving lights together into one wire and then splicing the two grounds from the headlights together into one wire. I dont think this would be a problem here, but I cant find information on then splicing these two wires together into a single wire effectively merging all four grounds into one ground wire by the end of the harness.

Im trying to avoid grounding to the chassis in this auxiliary wiring harness I am planning out and would prefer to either make my connections via a grounding terminal or directly to the negative battery terminal.

I know for my sniper EFI, the battery hot and ground will be connected independently to the battery to prevent issues. But with this whole harness I am building I am looking at roughly 12 ground circuits and trying to reduce the number down where possible, I can reduce it down to 6 ground circuits if I link all the grounds on the relays together via daisy chaining terminal 85 to ground. Id like to get it down to 3 to 4 ground circuits by time I get back to my fuse/relay box connector.

 

You can combine the grounds like that, as long as you take into consideration the current draw for each circuit. Most people think electricity does it's job when it gets to the device, and then there is nothing much left. They don't realize that the current in the circuit is the same no matter where you test in the circuit. I am not saying you don't realize this fact, just putting it out there for everyone to think on.

So if you have a light that draws 5 amps the ground will have 5 amps on it when the light is being used. Combine that with another 5 amp light, then the combined ground wire will have 10 amps on it. And it keeps building from there. You can also have voltage drop in the ground wire. So you don't want to run very thick power wires to avoid voltage drop, and then run puny ground wires, they will introduce voltage drop also and have the same affect as a undersized feed wire.

 

Thats what I was thinking but wasnt sure if I was thinking along the lines properly.

The lights I did the math on and what I have is as follows.

Headlights : 110W/120W @ 12.8V = 8.6A/9.38A / @ 14.0V = 7.86A/8.57A
Driving Lights : 200W @ 12.8V = 15.63A / @ 14.0V = 14.28A

Worse case at nominal battery voltage of 12.8V with most current draw I am looking at 25.01A.

If I run a 10 AWG ground wire like I was going to run from the battery to a junction block I would be good at 25.01A for 11' 5" which I doubt I am looking at 11' from the lights to the battery. At 30A with a 10 AWG wire I am still good to almost 9 1/2'.

My headlight and driving light power wires are going to be 16 AWG. The grounds were going to be 16 AWG as well, but what I was thinking was work my way up with each merge so like my Driving lights two 16 AWG wires spliced together and the other end of the splice would be a single 14 AWG wire. Same with the headlights then when the two 14 AWG wires splice together the single leg would be 10 AWG. In my mind this says it should work but on paper if I merge two 16 AWG wires together the effective gauge of the two wires is 13 AWG so I should run a 12 AWG wire after merging the two 16 AWG wires together. If I use 13 AWG which doesnt exist it comes up that two 13 AWG equal to a single 10 AWG, but if I use two pair of 12 AWG I am looking at 9 AWG. So the end goal of a 10 AWG should be well over enough based off what I am figuring for the circuits I am dealing with.

So in theory I should have no problem, with the cost I am looking at I am triple checking cause I am looking at a good amount of money for the connectors I am looking at and the pins so I have to size everything right. Like wise if I reduce the ground wires down I can go with a smaller harness connector.

 

Looks like you have got a handle on it.

 

Sorry to hijack this thread but I'm curious whether a flat braided ground cable as opposed to an insulated single cable would be preferred in such a grounding situation?

Seeing the many flat braided ground cables from the manufacturer makes me wonder why they're used?

 

I always thought braided grounds were for rfi purposes but other than that there isnt much difference. (In autos) Besides price that is.

 

Not sure why they used the braided cables, but in all the applications I have seen they are fairly short runs. He will be making long ground runs, so I think regular insulated wire would be best.

He is basically changing his wiring around to be more like a Corvette, where most grounds have to be run all the way back to complete the circuit. This makes sense where you have corrosion problems and can't rely on the body and the frame for a good connection. Actually Ford did the same thing on some of their vehicles. I think we have determined sometime in the mid 80's they ran a dedicated ground wire from the rear taillight area on their trucks all the way up to the front and bolted it behind the radio on the firewall.

 

^^^That makes sense and thanks for the ideas!

 

Braided cable is best used for block to chassis/block to body grounds. The purpose of the braided ground straps is that they support higher amperage, better heat dissipation and are very dependable with linear and lateral motions as well as vibrations.

I dont know if RFI purposes was a reason I know they can carry more amperage and they are more dependable in areas where movement happens.

Correct, in my case the core support grounds are probably adequate for my headlights and driving lights, but I want to maximize performance thus running the grounds back to either a terminal block on the side of my auxiliary fuse/relay box or directly to the battery itself. In the case of my sniper it is stated to run power and ground directly to the battery to prevent RFI issues which has me wondering would connecting to a terminal block be the same if the battery is supplying power/ground to the terminal block directly.

 

The sniper people are worried about ground loops. That is where one grounding point is a little better than the other. When that happens, you get small currents in the ground wire itself, which is basically noise and can cause problems with sensitive electronics. If you run large enough grounds, that should not be a problem. But in their case they do not want someone grounding the fuel injection system to the body somewhere, and the ground not be as good as the battery ground.

 

Correct, they want to use the battery as a capacitor to filter out the noise and poor grounds allow the battery to not work as a capacitor to filter the noise out. I will be running the grounds just like factory from battery to block with a ground strap from the back of the head to the firewall for starters. I will then run a ground strap from the block to the frame.

As far as the sniper goes I just rather run it to the battery or close to the battery without having something in between that can cause me issues. Ive installed numerous snipers over the years at work and never had one with RFI issues as I have always made my power and ground connections at or close to the battery itself and not just a sheet metal screw into the firewall for ground and piggy backing the battery hot off something like the alternator itself.

 

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On electrical wiring for a house or commercial property, the ground is a fault path. The ground sits there and does nothing, unless a hot wire touches a grounded metal part. It then sends a fault current down the ground wire and that trips the circuit breaker.

 

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While that might be true of AC circuits grounds are VERY important to a 12V DC system such as found in automobiles! They are literally one half of the electrical system, a half that when missing or faulty cause issues.

 

yep remove the ground from a tail light or a sending unit and see how well it works. AC is a different beast from DC. Guess it needs to be said?

 

That would appear to be the case!