Is a ground still a ground

T

tommyleea

Senior Member
Positive ground question. For example if I had a map light I wanted to install, and it had a positive terminal and a negative terminal. Would I still just ground the negative terminal, even though it would go to the positive side of battery? I don't think I will ever comprehend this...Thanks
 
pretty simple if you read you question back to yourself.you answered your own question positive ground is positive ground plain and simple
 
If the battery is positive ground all components of the electrical system will be positive ground. If the battery is negative ground, then all electrical components are negative ground. A light will work either way.
 
If the dome light fixture has separate wires labeled positive and negative, connect the positive wire to the body of the car and the negative wire to the power source. Especially if it's an LED light fixture, they are polarity sensitive and won't work if connected backward. A regular incandescent bulb won't care.
 
Think of it this way, a direct current electrical system operates through a chassis and a load (the load could be induction or resistance type, anything that consumes power).
The chassis (body, frame, engine block, etc) is normally used as the ground source for car electrical systems, while the load (light bulb, electric motor, resistance heater, etc) is assigned as the electrode.
A battery is neither positive, nor negative ground. Ground is whatever is being used in the electrical system.
In pre 1956 cars, the positive terminal of the battery was assigned to ground (body, frame, etc), while the negative terminal was assigned to the load terminals.
In 1956 and later cars, the negative terminal of the battery is assigned to ground, and so the polarity is the opposite of what was used in previous decades. Of course, the polarity of the generator is assigned to match.
So in a negative ground system, the negative terminal of the battery is connected to body, frame, engine block, etc.
The ground system is a return path back to the source (battery).
 
Current flows from positive to negative. It is directional. It don't matter which terminal is connected to ground (the chassis), current still flows from positive to negative. The many devices in a vehicle need to be divided into which ones care about the direction of current flow and which ones don't.


Simple answer, light bulbs don't care, switches don't care and for the most part relays don't care. Instruments do, motors do, radios do and of course the generator/alternator care.
 
I have the feeling that if I touch the car I will get shocked. Can you still have a braided ground wire with positive ground? When I use my test light do I connect the clip to the positive battery terminal instead of negative terminal? These are the questions that keep me awake at night.
 
tommyleea said:
I have the feeling that if I touch the car I will get shocked. Can you still have a braided ground wire with positive ground? When I use my test light do I connect the clip to the positive battery terminal instead of negative terminal? These are the questions that keep me awake at night.
Click to expand...
Shocked if you touch the car? Only if you're touching a bare (or bad) spark plug wire or terminal while the engine is running, that will knock you back on your butt because the voltage is very high. 15,000 to 30,000 volts depending on what ignition system the car has.

Keep you awake at night? don't watch this video :rolleyes:
https://www.youtube.com/watch?v=fPoomwdNZeY
You can ask me why they don't instantly get cooked.

A bare braided ground wire? Is perfectly fine, it's just like any other bare metal that's part of the body of the car. You won't get shocked unless you or part of your body are completing a circuit from one side of the power source back to the other side.
AND except for the ignition system the voltage in car wiring is so low compared to the resistance of your body there is no current flow, or it's so slight you won't feel it. Example: With dry hands you can touch the + and - terminals of a 6 or 12v car battery at the same time and not feel a thing.

Test light? It's like hooking up jumper cables to jump-start another car. Positive terminal to positive and negative to negative.
I'm not sure what the clips on your test light look like or what kind of bulb it has but if the wires are Red and Black, the red is positive and black is negative.
.
 
Last edited:
dmsfrr said:
Shocked if you touch the car? Only if you're touching a bare (or bad) spark plug wire or terminal while the engine is running, that will knock you back on your butt because the voltage is very high. 15,000 to 30,000 volts depending on what ignition system the car has.

Keep you awake at night? don't watch this video :rolleyes:
https://www.youtube.com/watch?v=fPoomwdNZeY
You can ask me why they don't instantly get cooked.

A bare braided ground wire? Is perfectly fine, it's just like any other bare metal that's part of the body of the car. You won't get shocked unless you or part of your body are completing a circuit from one side of the power source back to the other side.
AND except for the ignition system the voltage in car wiring is so low compared to the resistance of your body there is no current flow, or it's so slight you won't feel it. Example: With dry hands you can touch the + and - terminals of a 6 or 12v car battery at the same time and not feel a thing.

Test light? It's like hooking up jumper cables to jump-start another car. Positive terminal to positive and negative to negative.
I'm not sure what the clips on your test light look like or what kind of bulb it has but if the wires are Red and Black, the red is positive and black is negative.
.
Click to expand...

Thanks for the video. I always did like the Tesla coil presentation. Not that I was there. I guess test light probe is more correct. To see if power is present at a certain point. Like test an installed fuse to see if there is power. I am used to just grounding the clip, and then touch the probe to the fuse and see if it lights up or beeps. Thanks again for the help.
 
tommyleea said:
. . . I guess test light probe is more correct. To see if power is present at a certain point. Like test an installed fuse to see if there is power. I am used to just grounding the clip, and then touch the probe to the fuse and see if it lights up or beeps. Thanks again for the help.
Click to expand...
If it were polarity sensitive it wouldn't work when hooked up backwards. If it works just use it like you have been. Not a problem.
 
bobss396 said:
Most older cars had a braided + ground cable on them. Ground is ground no matter what you call it.
Click to expand...

Thanks..I am trying to revise my thinking to power and ground instead of positive and negative. As per Flathead post..
 
Last edited:
You must log in or register to reply here.
Back
Top