12g wire for grounding harness?

[NovacaineFix]

Back in the days when I was a auto tech, I would run into this from time to time (grounding issues).

It is one of the most overlooked items on any vehicle with an engine, battery and charging system. Even more complicated with computers and electronics.

May I suggest using multiple grounding straps?
https://www.google.com/search?q=aut...ITKAhVL8mMKHSW5DoMQ_AUICCgC&biw=1487&bih=1242

12g wire and 10g for that matter, may be sufficient for some applications, but lends itself to failure fairly easy.
They way to think about grounding is not to ground thongs but to see it as a electron flow return back to the battery. Your return lines (ground straps/cables) should equal that if not be greater than the cable feeding your starter, just to be safe.

Here is a good example:
I had a Chevy Camaro that I rebuilt and replaced the engine for a friend/customer. Several weeks later, they complained that the floor shifter was hard to shift. I was thinking it may have had a broken mount somewhere. Looking at it, and shifting while the engine was running, I noticed sparks within the shifter console. I checked the mounts anyway, just to be sure, nope rock solid.
While the car was up in the air, I did notice that a ground strap had broken off, the eyelet was still attached, but no cable.
The shifter cable was no acting as the ground, since it was the last thing that was metal that was not insulated from ground.

Replaced the ground strap and shifter cable, problem solved!


Remember not all metal items are fully grounded. The engine is not, the engine mounts insulate it from the chassis. You have to use a strap(s) to provide that path to chassis ground back to the battery. I would use multiple straps if you have the room, this way you provide path to ground than needed and also create redundancy if a strap corrodes or breaks.

 

[tim292stro]

There is some good info on this link for your installation. I'm not positive but I wouldn't think using 12 instead of 10 would be a big deal on this application. http://www.hummerknowledgebase.com/electric/hghi.pdf

*Sigh* that's what I thought. Right, so the Kascar wire harness is intended as an electrical ground return path to either supplement or replace the factory ground harness.

I think I may have been a little muddy in explaining what I want to do. That's my fault. I want to make the harness that kascar sells and everyone recommends installing. I have seen how to make it explained on flashoffroad but I think he uses 8 or 10 gauge wire. I'm not replacing any existing wires. I just want the mentioned grounds grounded to the back of the engine like the kit is supposed to. I could just buy the premade kit but I can't spend the $70 right now. This is a cheaper option right now.

The Kascar harness is underdsigned if it goes to the devices you say it does - that's my warning. You can duplicate it 1:1, but again it's underdesigned.

Bonding can mean "attach, secure" and that is what I meant.

Jeeeze...thank you Ted....just buy the harness from kascar, no fuss, all done.
i used to make mine, while maybe at 1/2 the cost...but my time is worth more then the 40.00 I saved.

Harness is Prestolite 10 gauge, 1oz. wire. It's for bonding all components, not made for loads.

I'm going to disagree with the three of you here and go back to my original comment:

EEEKK!!! That needs to be MUCH larger than 12Ga/10Ga. The generator (alternator, 100Amps), and starter (up to 1500Amps) will ground through the engine, but steel has about 10% the conductivity of copper (and power has to jump through gaskets and bolts). From the negative post of the low 12V battery, go with a 2 gauge or thicker wire to the alternator, 0 gauge to the starter, and 8-10 gauge to the engine block itself and another 8-10 gauge for the PCB (where all the power for the rest of the chassis splits from).

Reason for this is: the factory is looking for good enough to last the warranty period and cheap enough to win the contract. Almost 100% of the time a factory electrical system is undersized as a calculated risk for the sake of cost, weight, and wear. I like to use Honda as the poster-child for under designing an electrical system - they are so focussed on cost savings that they will deliberately undersized systems, go measure the voltage at the brake light socket (with the bulb in and working) for yourself if you have a Honda, more than 10% drop on all circuits. The HMMWV is a special case with its fiberglass hood and aluminum body on the steel frame - they can't do a straight metal to metal electrical connection as it would corrode in no time, thus a dedicated ground harness is required as an electrical ground return path.

Back in the days when I was a auto tech, I would run into this from time to time (grounding issues). It is one of the most overlooked items on any vehicle with an engine, battery and charging system. Even more complicated with computers and electronics...
...12g wire and 10g for that matter, may be sufficient for some applications, but lends itself to failure fairly easy.
They way to think about grounding is not to ground thongs but to see it as a electron flow return back to the battery. Your return lines (ground straps/cables) should equal that if not be greater than the cable feeding your starter, just to be safe...
...Remember not all metal items are fully grounded. The engine is not, the engine mounts insulate it from the chassis. You have to use a strap(s) to provide that path to chassis ground back to the battery. I would use multiple straps if you have the room, this way you provide path to ground than needed and also create redundancy if a strap corrodes or breaks.

NovacaineFix is basically seconding what I said earlier about the grounds in a vehicle. There needs to be a return path. Galvanic insulation from Aluminum bodywork to Steel framing is also electrical insulation - there needs to be a return path to the battery. Body mounts and drive-train mounts are non-conductive, so there needs to be a ground return for this gap. Any corrosion in the body or frame adds more resistance to the ground return path, using a ground cable to return to the battery gets around this.


So, if you're sizing a DC electrical ground system, you need to size it like you're doing the positive electrical system, or the ground system will become your choke point - you don't want a "token ground system" where it's more of a check-box than a proper design. Wonder why electrical gauges in HMMWVs are notorious for being inaccurate? Might have a lot to do with the gauge and sender being designed assuming no ground issues, versus being installed in a truck full of ground issues...


If you have the basic 100Amp alternator both your positive and negative cables should be sized to carry 100Amps * 1.25 (125Amps) continuously, if you have changed the alternator or added loads not in the original design, you really should re-evaluate the electrical system to make sure you're not overloading anything. If you are pulling a ground strap for the engine/heads to ground the starter and glow plugs, bigger is better here (at least as NovacaineFix says bigger than the positive - that makes the positive wire and it fuse the safety trip, rather than the ground wire), so that all of the voltage drop happens across the load device rather than the metal in the block or heads. Head gaskets and bolts are not as good electrical conductors as copper wire (only about 10% as effective).


I'm not trying to pick a fight, but I'd prefer people genuinely understand what it is they are trying to do than have someone just say "it's good enough" without backing it up with sound engineering practices. Search Google for Circular mils per amp rule - you need at least 300cmils/amp to prevent the wire from overheating.

...Remember not all metal items are fully grounded. The engine is not, the engine mounts insulate it from the chassis...

This is also a point as to why I bring up RF grounds. If the OP is trying to run a radio of basically any kind (AM/FM, CB, HAM, etc...) RF bonding is very important. Every metal panel must be bonded to a common ground point with a strap material that has good RF carrying properties. A common round electrical ground wire is not a good RF conductor as the higher frequency the RF is the shallower in a cable it will penetrate (called the skin effect). A wide flat strap is shallow over its entire cross-section for a given amount of copper used. All electrical devices with motors, armatures, brushes or any kind of semiconductor parts must be suppressed with either chokes, bypass capacitors, or suppression diodes.

I have seen vehicles that had transmitting radios in them, where after a mechanic removed the RF bonding straps during a service job the owner wondered why they radio was noisier and wouldn't transmit as far... Sometimes these straps get removed during maintenance and never replaced, other times they just wear out due to corrosion and vibration, or mechanical damage (trail or road debris).

 

[o1951]

An electrical supply house should have most any gauge and color wire you need, along with crimp connectors, eyelets, etc. Probably the least expensive source for quality wire.
For general wiring, I use MTW wire - Machine tool wire - it is fuel and oil resistant. Where I have to connect to moving parts - Gen, engine, trans, I use fine wire straps for ground, fine strand wire for hots. You need fine strand ( like the wire used in an extension cord) so the wire does not fail from movement. I try to avoid welding cable because what I have seen is not fuel or oil resistant, and breaks down in under the hood applications.

I also solder all connectors to keep moisture and hence corrosion out.