Disconnecting and Reconnecting Car Batteries

When carrying out any electrical work to your car, it is usually necessary to disconnect the battery first. This brief guide will explain the best way of going about this. Disclaimer – always check your manufacturers handbook for instructions to locate and disconnect the battery as each car differs. Rubber gloves may be handy to prevent and grease, oil or electrical sparks during this exercise. If you’re worried at all about the procedure do not hesitate to contact a car mechanic to help you.

car battery

Locate the battery

You should find the battery is a rectangular box under the bonnet of your car. However, many newer cars now have a cover for the battery (with a battery symbol on top of it) which you will have to slide off or lift up to locate the terminals. If you’re finding it difficult to locate the battery, try reading your handbook for the right location.

Recognising positive and negative/ground terminals

Next it’s a good idea to discover which terminal is positive and which is negative. The general rule of thumb is the positive terminal will have a ‘+‘ sign on it and the negative terminal will show a ‘‘ symbol. Sometimes you may also find the positive has a red cable colour and the negative a blue colour but please double check your handbook in case this differs.

Negative first

It’s important to disconnect the negative side of the battery first, otherwise you can cause an electrical short if the positive is removed first. For instance, if you accidentally drop a spanner on the positive terminal and the spanner touches anything else that’s metal on the car you’ll create a circuit and short the battery, or even worse give yourself an electrical shock. To remove the negative cable, loosen the connector and carefully wiggle the clasp off the terminal. Next remove the positive connector in the same way. Handy tip –  to prevent the connectors touching anything else on the car whilst they’re disconnected, get a plastic tie or similar and attach them to something which keeps them out of the way and not touching anything metal!

Reconnecting the car battery – positive first

Once you’re finished with the electrical work on your car, you can go ahead and replace the connectors back on to the terminals. Make sure you start the way you finished, reconnecting the positive terminal first and then the negative afterwards to prevent short circuits. Push the connector back on and give it a good wiggle to ensure you have a snug fit. Try to prevent touching any other metal work on the car with the negative connector. You may notice a small spark when reconnecting the negative terminal, but this is normal and shouldn’t be dangerous. You are simply starting the electrical circuit again in the car.

Cover the battery and close the bonnet

All that’s left now you’ve reconnected the battery is to replace any battery cover(s) you removed at the beginning and then close your bonnet. Hopefully the electrical work you’ve carried out has been a success! If you find you haven’t got any electrical power, check the terminals are clean and free from dirt and try again. Failing that, you may have shorted the battery if you touched the negative terminal on any of the car’s metal work.

If you need further advice on your car’s battery or anything electrical, MCM Garage are happy to help. Just give us a call today on 01761 415 501 or contact us via our online form and we can set-up a quick appointment.