Ground Bus

[Farrar]

Think of killing an ant with an atomic bomb....

A friend of mine likes to say "Overkill is underrated."

[Bitsyncmaster]

Your starter also relies on the contact of engine to ground it. The extra ground wire just provides a path if the contact surface was not clean or the bolts are loose.

[Nicholas R]

I'm no electrical genius, so can someone please explain to me how grounding the alternator via a cable is better than grounding the alternator via the engine? How does cable > engine in this instance? Thanks in advance.

Personally I don't think it is. I don't know of any production vehicle that doesn't simply ground the alternator through the housing of the alternator, to the engine block. Older vehicles with external voltage regulators may be different, but any modern single wire alternator grounds through the alternator housing.

[FABombjoy]

I'd guess the only exception being if you engine ground strap rots out. Isn't that what sets shift cables alight?

I did add a cable from the alternator housing to the frame. It was cheap & easy as my CS130 alternator already had a ground cable/strap bolt. I wouldn't have gone out of my way to add one tho.

Ground wise, this is what I did:
-Alt case ground - because cable was cheap & flat was there
-4ga lead from the bulkhead bolt directly to the battery - The ground wire connecting to the bulkhead bolt to the frame seemed flimsy to me considering how close the battery is.
-Additional block ground strap on drivers side - Easy to do when changing the motor mounts

+12 side:
-I binned the triple brown alternator wire world tour that runs across the top of the engine. Jump lead is now connected to the +12 bulkhead bolt in the '83 style

Basically just skosh of cheap overkill.

Megasquirt voltage & sensor logs are clean as a whistle. Audio system (amp connected directly to the bulkhead bolts) has no perceptible hum/buzz/whine/etc.

[Ron]

I'd guess the only exception being if you engine ground strap rots out...

And guess what the starter is going to try drawing 100++ amps through ;-)

I binned the triple brown alternator wire world tour

That and a cable connecting the block directly to the battery should be on any D upgrade list, imho!

[Shep]

I'm no electrical genius, so can someone please explain to me how grounding the alternator via a cable is better than grounding the alternator via the engine? How does cable > engine in this instance? Thanks in advance.

Personally I don't think it is. I don't know of any production vehicle that doesn't simply ground the alternator through the housing of the alternator, to the engine block. Older vehicles with external voltage regulators may be different, but any modern single wire alternator grounds through the alternator housing.

Just so everyone's on the same page, electrons flow from ground to positive. The mix up was because some idiot way back when flipped a coin and got it wrong and we all hate him forever for it. Anyhow. When you're trying to water your flowers, do you turn the spout on and hope it will eventually reach your flowers, or connect a hose first and at least guide it to the flowers? Same principle here. It works without a hose, but it's not at all efficient by any stretch of the imagination.

Ron's bit on the starter is spot on with the reasoning as to why the Big Three is around at all. It increases efficiency of the electrical system by allowing surge current and voltage to flow unimpeded. Ever had a low battery cause a difficult start? Same basic concept: the overall capacity isn't there. The system struggles to get enough current from the battery to start the car. With the car's wild mix of metals and material choices along this grounding path, there's not much sense in reinventing the wheel. Engines are aluminum, frames are steel, painted with epoxy, wires are copper, even the electrons don't know what the hell they're doing. Start to finish one-piece wire eliminates any question marks, maintains reliability, and provides an easy path of least resistance.

So, why don't production guys ground with wires by default? They... actually do, I don't know what makes anyone think they don't. Alternator grounds to the engine. Engine grounds to the frame. Via a wire. The Big Three leaves that ground wire for spark plugs, ECU, transmission governor, etc. functions alone and instead adds a new wire bolted directly onto the alternator mount. The alternator is creating electricity, so it really needs its own set of grounds to battery and frame. The reason automotive manufacturers aren't squeezing 100% electrical efficiency out of their cars from the factory is extra cost for zero benefit for them. 99% of the population daily drives their cars and doesn't care about this stuff. Why cater to the 1% of customers that do, and will likely redo it anyway? Much like putting plastic speakers in the cars, nobody cares enough to say they sound horrible because it sounds fine to them.

I know I redid my car's attempt at the Big Three though. My 2017 Kia Optima has a wire grounding the battery to the frame within 12 inches. But with 8 AWG, it wasn't long at all before I upgraded it, and extended it also to bolt to the alternator at the frame mount. While not ideal (it's missing the alternator-to-battery wire), I will have to revisit at a later date when I can get a new battery in the thing. Yes, it's new, but lead acid batteries are a whole 'nother shitfest of their own.

[Farrar]

Thanks for the info. 👍

[NckT]

7 pages of posts to add extra earth (ground) points, when all that is really required is to clean up any high resistive joints on the original wiring on the car.

[Shep]

7 pages of posts to add extra earth (ground) points, when all that is really required is to clean up any high resistive joints on the original wiring on the car.

God no, nonono no, don't encourage bad behavior, that's like brushing your teeth and leaving the cavities alone, then chowing down on a bowl of popcorn kernals mixed with ice. None of that is even remotely close to a good idea. It's more akin to a band-aid on a broken femur than a legitimate solution to a design flaw.

I don't think anyone at any point in this thread has said that only cleaning up "high resistive joints" alone is a even close to a wise idea for good reason. The first post was about laying down new ground wires to compensate for the undersized OEM ones. Where the notion came from that the car's grounds are properly designed is beyond me but they are anything but.

Steel is tolerable as a wiring path, but only if properly cared for. McFly himself saw exactly why grounding through the easily-rusted frame is a horrible idea. Modern manufacturers do it because unibody designs inherently mean that frame and body are one electrical channel. That's why batteries often ground to the mating section between unibody and frame. And it's also why said ground is physically built far away from potential sources of corrosion, which places it under the hood of the car.

The DeLorean did a lot of things wrong with the electrical approach by design. First, the frame is the only stretch of wire front to back in some ground loops. This is a terrible idea when high current devices (headlights, fans) are using this very same path. A chain is only as strong as its weakest link. The mere fact that the weakest link needs occasional redoing to keep pristine speaks volumes.

Bear in mind also that automatic frames have a different current capacity than manual frames thanks to the transmission shifter cutout. It's equivalent to a kinked pipe, there's an immediate loss in capacity at that spot. I'd personally estimate that section of frame gives an equivalent AWG size between 1/0 and 2 for copper wiring, given the difference in metal as well as conductivity of copper vs. mild steel, as well as a corrosion factor to accommodate most frame conditions.

This was an area that DMC would have worked out had they been given adequate time and resources to do so. I'm convinced that Johnny Carson's infamous hitchhiking could have been at least partially alleviated with more focus on the electrical system. Some who have crunched the numbers have stated the alternator was more than capable of handling the load, and wondered why it didn't. What's forgotten is the current doesn't travel to the front that well, which is exactly where all the power was being used.

[Bitsyncmaster]

I did run an extra ground wire on the drivers side frame to engine mount but that was because I could not verify the passenger side was clean and a good ground.

The one ground I found that was a poor design was the fuel pump current sharing the ground for the gauges. The added current from the fuel pump creates a voltage offset for the gauge ground. Hence our volt gauge reads about 0.3 volts to low.