If you need to jump-start the vehicle or replace a battery, it’s important to know how to properly but safely disconnect and connect battery cables. Which battery cable should be removed first but installed last? If you can’t identify the correct answer, you could hurt yourself.
In this article, I’ll go into more detail to explain the reason to take the negative cable off first. I’ll also help identify the two battery cables and detail in-depth why this step is important.
Identifying Battery Cables
The battery terminals in your car are probably marked or color-coded. If they are marked, you’ll see a plus sign on the positive terminal and a minus on the negative terminal.
It’s also likely that the caps are color-coded, in which case red means the positive terminal and black defines the negative terminal. If you’re lucky, your car may have both markings and colors to make them easier to identify.
Read More: How to Tell Positive and Negative Terminals on a Car Battery
Which Battery Cable Should Be Removed First?
Always disconnect the negative cable first, and reconnect the negative last. If you disconnect the positive first, you could create an electrical short and sparks, particularly if anything metal touches the area. You must take battery precautions to ensure safety.
You will need to use a socket wrench (normally 10mm) to disconnect the battery cable. Make sure it fits on the bolt of the connector. Turn the wrench counter-clockwise, and it should loosen. Just never allow the socket to touch a battery terminal. If you the socket touches both terminals at the same time, you create an electrical pathway.
When you take the negative cable off, you will want to put it aside. You must ensure that it does not touch the battery or the positive terminal.
Which Battery Cable Should Be Reconnected Last?
The negative battery cable goes on last, and the positive cable goes on first. When installing a new battery or finishing jump starting a battery, you’ll need to make sure you reconnect it in the correct order.
If you remember the steps during terminal removal, you would just do everything back where it started in reverse.
With this in mind, and knowing you connect the positive terminal first, you are now ready to affix the negative terminal last.
Why Disconnect Negative First?
If you don’t take off the negative connection from the battery first, you risk an electrical short. Suppose you drop a metal tool on the positive terminal and it touches anything metal on the vehicle; in that case, you’ve created a circuit where electricity can flow at two places.
This problem will short your battery. It can also give you one heck of a shock. That’s why the negative cable should always be the first off and the last back on.
It’s just as important they do not touch one another or anything else when they’re off. Some people use a plastic zip tie or something to attach them somewhere out of the way. Just make sure you don’t let them touch anything made of metal.
Once you’re ready to reinstall the connections, you can cut off the zip ties. Just remember, positive first, always negative last, give them both a good strong wiggle to make sure they are seated for the best connection.
Stay calm when you see a little spark when putting the negative connection back on. It just shows that you made a connection back to the electrical circuit.
What happens if you disconnect the positive terminal first?
While it is possible to disconnect the positive battery terminal first, it is unwise – it might damage your vehicle, or hurt you!
While undoing the cable lead, you might unintentionally touch a chassis or another part of the car with a spanner (or your body) while undoing the cable leads.
Because the negative battery cable is still connected, this creates a short circuit, which could destroy the battery or even damage sensitive electronic parts.
Can you just disconnect one battery terminal?
Yes, but make sure to disconnect the negative cable. This will completely sever the car’s entire electrical system away from its source of electricity, which is needed when you’re doing work around sensitive electronics such as sensors or control units.
Just don’t allow the cable to fall on the terminal of the battery while you’re working on the vehicle. The cable can be secured by zip-tying it to a nearby piece of formed plastic or anything else that is not metal.
Why do you connect the positive terminal first?
Reconnect the positive battery cable first to avoid short-circuiting. This is something that can happen if a spanner touches the metal of the car while tightening up the battery clamp.
You can protect against this happening again by just leaving the negative battery cable disconnected when reconnecting the positive battery cable.
However, you could safely reconnect the negative battery cable without runway battery wire from touching something else, because the battery cable is already connected to the metal of the car chassis.
Is it OK to just disconnect the positive terminal?
No, it is not fine to just disconnect the positive terminal or do it first when removing the battery. If for example a piece of metal such a wrench accidentally bridges the battery post and the metal parts of the chassis an electrical short circuit could occur.
This would then possibly kill the battery and fry an expensive component. Similarly, going from an electrical floor to connecting the wrench would give you an electric shock; and there is also a risk of battery explosion.
Unhooking the battery can seem simple – unhook the terminals and disconnect the cables. There is only one right way to do this: you unhook the terminals; and that is to remove the negative terminal first.
That is to avoid bridging the battery post and chassis and the electrical short circuit for which would attempt to kill the battery or fry an expensive component (the wrench slipped, an electrical flow stunned you, and exploded the battery).
So the first thing for when you decide to disconnect the battery would be to locate the negative post or terminal, which is signified by the minus (-) sign on the top side of the battery. You will also need a proper socket or wench; this in most vehicles around the 10 mil size.
Once the cables are disconnected from the battery you will want to make sure you secure the cables so they swing about and make contact with one another. The most convenient solution is to use a zip tie or something of that nature.
Finally when you reconnect the battery your order is reversed. Cable to the positive terminal first, secure and don’t touch the negative terminal.