Alam has the reason, eliminate 'most' of the short possibilities.
If you put a wrench on the POS terminal with the NEG still connected pretty much every metal piece within reach of your wrench would cause a pretty serious short.
IF you first disconnect the NEG the only place you could short to in most vehicles would be the positive terminal itself. If you hit the wrench to any other metal part of the car while its on the NEG terminal worst thing that will happen is it will re connect the NEG terminal. Once the NEG is off it won't matter if the wrench on the positive terminal hits anything other than the actual neg terminal on the battery itself.
THIS IS WHY !
A factory trained tech has a service manual.
it is also why you must say what you are working on to get correct answers from this website.
If your vehicle has backup power supplies, for systems which function even after damage during collision,
You must power them down.
For example, SRS, or airbags. the Positive is removed first.
If you are concerned with your wrench touching ground while turning a connected positive, insulate it from touching.
Only trained personel are qualified to repair and maintain your vehicle properly.
If you want to simplify and save money, that is.
If not, You can replace several items and then start asking questions without identifying the work.
Then blame someone, is the established norm, unfortunately.
Cars before SRS for example, were also negative ground.
You were safest and had less thinking to do when removing the neg. first , and replacing it last.
It never hurts to obtain the manual for the vehicle, and review it.
They are not All the same in their schematics.
If you are replacing or maintaining the battery and its cables you can remove negative first and touch nothing else till the operation is complete. meaning, no keys in it, no doors open, just the hood, and replace the battery, reconnect, then restore systems. This can be safe even with variations in your system.
Historical note:Cars in 1954 and before could be positive
ground.
German and other Bosch fuel systems , you unplug the fuel computer first. Before any electrical work.
And so on...
Ground cable then positive cable before removing the battery.
When removing the battery, the NEG first, then the POS.
When installing the battery, the POS first, then the NEG.
Reduces the chance of arcing and sparking when disconnecting and reconnecting the cable to the POS terminal.
The negative first. A positive charge can be gained via an arc even after you remove the clamp, but a ground requires contact. Once you remove the ground nothing else can happen but the same cannot be said if you remove the positive first.
Always remove the Negative cable first.
Positive cable.
NEGATIVE!!!!
EVERY CLASS I EVER TOOK SAID NEGATIVE FIRST. THINK ABOUT IT, IF ONE REMOVES POSIIVE FIRST ANDT HE TOOL SLIPS, THE TOOL WILL CONTACT GROUND AND ARC. IF FOR NO REASON OTHER THAN SAFETY.....
Besides since electricity always takes the shortest path to ground! to prevent spiking control units it's the logical choice again!!
RETIRED ASE MASTER TECH
Negative first. Once you disconect neg. You eliminate most of short circuit possibilities.
first negative then positive cable
The black earth cable.
negative, it will have far less chance of a spark and since a draining battery will produce hydrogen or at least release it, that spark can ignite that.
Put on the red then the black. Take off black then red. Its not "hot" till the ground (black) cable is attached.
You know if a person has to ask this question they really should not be working on a car!
Negative first. Once you disconect neg. You eliminate most of short circuit possibilities.
ALWAYS: ground (neg or -) cable first, hot (pos pr +) one second. To reinstall, invert order.
Ground or negative first.
positive on first, positive off last
It does not matter, as you can tell by the contriving answers ?
Right answer
neg [-]
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