Why automotive grounds are important.

[WP29P4A]

Traditional clapping requires your left and right hand working together, properly working automotive electrical requires both positive and negative working together to make devices work.

The grounds on your truck are required for your electrical to work properly. The grounds in your house are a backup to make electrical safer, almost EVERYTHING in your house will still work WITHOUT a ground. Virtually nothing on your truck will work without a ground.

The distribution of voltage starts at the positive terminal, travels through wires to get to your fuse block, then gets distributed to the devices (lights, radio, engine, etc.) Think of the electrical path as a circle, that starts and ends at the battery. The path HAS to be complete for the device to work. The path returns to the battery through the body and frame of the truck, they do this to reduce the wiring by half.

Your trucks have rubber isolation mounts between body and frame, which is why you had ground links between the frame and body/bed, and from frame to battery and body to frame or battery and from battery to engine, linking ALL the body panels and frame together, with the negative battery terminal.

If you are trying to trace a bad ground, make a long test wire with alligator clips on both ends, clip one end to the battery, and touch the other end to the negative side of the circuit or device you are having issues with, if the device starts to work properly, you have confirmed a ground issue.

 

[Blue Ox]

Would it hurt your brain if I told you DC actually flows from negative to positive?

 

[WP29P4A]

Would it hurt your brain if I told you DC actually flows from negative to positive?

Not really, thought that would just make my point more confusing. Regardless of the direction the electrons flow, the distribution of power is from the positive side of the battery, separated into circuits and fused before heading to each device, then grounds connected in common to complete the circuit, back to the battery.

If people are struggling to figure out the basics of automotive electrical, like why grounds are important, adding something not really useful or logical, seemed like TMI.

To be honest, I did not remember that electrons in DC voltage flowed from - to +, I haven't played with an Oscilloscope since junior high school.

 

[SirRobyn0]

Doesn't matter which way the electricity flows as long as folks realize there is a flow and negative is just as important as ground. Lots of guys, even some mechanics I've met seem to think negative is not as important as the positive, and for example they can't understand why a starter is struggling to turn an engine over....

The grounds in your house are a backup to make electrical safer, almost EVERYTHING in your house will still work WITHOUT a ground. Virtually nothing on your truck will work without a ground.

I learned 12 volt electrical before I learned the house stuff. And I don't want to side track your thread to much, but suffice to say that gave me a little trouble early on.

 

[skysurfer]

Would it hurt your brain if I told you DC actually flows from negative to positive?

What hurts my brain is thinking about that statement coupled with the fact that my '59 MGA has a 12v positive ground system. Hooking up a battery with the positive lead going straight to the frame always makes me turn my head a little and expecting lots of sparks and noise.

 

[Ricko1966]

Now to add a new point to ponder, learn how to do volt drop tests, positive side and negative side you will be very glad you did. There's more than just power and ground. There's good and not so good power and ground,a volt drop test will reveal this.It will demonstrate whether you have acceptable voltage when the circuit is actually in use,like a battery cable that has internal resistance it measures good with your meter but isn't good enough when under a load. Here's a good link

How to use a Multimeter, Part 5: Measuring voltage drop - Hagerty Media

During the past month, we’ve covered how to use a multimeter to measure the trinity of voltage, resistance, and current. I’ve explained how this covers most electrical diagnosis in a car—how most of the time, you’re either trying to verify the presence or absence of voltage to a device or the...

www.hagerty.com

 

[Blue Ox]

What hurts my brain is thinking about that statement coupled with the fact that my '59 MGA has a 12v positive ground system. Hooking up a battery with the positive lead going straight to the frame always makes me turn my head a little and expecting lots of sparks and noise.

Once upon a time that was more common. While technically more correct somewhere along the line we standardized on negative ground.

The real problem comes in if you're working on an older vehicle and don't realize it's positive ground. I was trying to do some diagnostics on an early 1970s Mack once and had to get creative when using modern electronic tools to do tests on it.

 

[Keith Seymore]

When I would investigate design problems I would always go directly to the Electrical Vehicle System Engineer.

I'd say: "Jerry - I've got a...."

and he would interrupt with "It's a bad ground".

I'd say "you didn't even let me finish my question!"

"Doesn't matter. It's always a bad ground".

K

 

[Keith Seymore]

When I would investigate design problems I would always go directly to the Electrical Vehicle System Engineer.

I'd say: "Jerry - I've got a...."

and he would interrupt with "It's a bad ground".

I'd say "you didn't even let me finish my question!"

"Doesn't matter. It's always a bad ground".

K

Sidebar #1: We became pretty good friends outside of work, since he lived in my same little community north of Detroit.

I would often be out in my shop, wiring something up, with him on the phone stepping me through it.

We actually discovered a build issue that way: the electrical architecture changed in 2003 with the new front end design. We didn't realize it but the electrical team changed the pinouts for the trailer brake controller without anybody realizing it, swapping two wires in the cavities. I found out I couldn't get my trailer brakes to work about the same time one of the other engineers coasted off the end of his driveway into traffic with his 1936 Cadillac in tow.

Once we figured out what happened we made a design change to the trailer brake controller jumper harness for 2003 and newer. If you look at the old harness and new harness side by side you'll see we changed the color of the connector from brown to white to help highlight the change.

K

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[Keith Seymore]

Sidebar #2: (More in line with this thread)

When I had my '80 stepside I would pull the tailgate and rear lamp brackets and paint them every spring to combat the rust accumulated over the Michigan winters.

After a few years it got to where the turn signals and rear lights weren't working right. I fooled with it for the better part of the summer before I realized the problem (you probably already know where this is heading):

Bad grounds.

The stepside design used little star washers to break the paint and create the ground between those old Grote tail lamps and the tail lamp bracket, and then from the bracket to the box post. Naturally that also introduces corrosion. The fact that I cleaned everything up and repainted and replaced the fasteners with stainless bolts and washers was killing my ground.

I added a specific ground wire from the base of the bulb inside the lamp, through the production conduit and down to the frame to finally fix this problem once and for all.

K