Hooked battery up backward now car won’t start

If your battery is hooked up backward, your car will not start. And you may grapple with the question, what causes a car not to start if a battery is hooked up backward?

The short answer is the inability of the start relay to function. Think of this remotely operated switch as an electrical helper that’s core to all of your car’s electrical processes.

This includes the flow of electricity from your battery to the starter, which is necessary to start the engine.

Solutions for Fixing the Above Problem

To resolve this problem, simply switch the battery cables’ terminals to their corresponding battery posts. For starters, these cables often come with either a positive terminal or a negative terminal.

You’ll know it’s a positive terminal if it features a positive sign(+) or a red cap/ring around it. A negative terminal, on the other hand, is characterized by a negative sign(-) or a black cap/ring around it.

The red cable(positive cable) should connect to the battery’s positive terminal, which is marked positive(+). The black cable(negative cable) should connect to its negative terminal, which features a negative(-) symbol.

What Happens If I Hook Up My Car Battery Backward?

Reverse polarity, which I’ll explain later, will occur. Consequently, this will fail to activate the voltage from the battery to the ignition coil to produce the engine spark as otherwise expected.

What’s more, there will be no engine spark from the coil or coils that would otherwise be directed to the spark plugs to ignite the fuel to start the engine.

What Happens If You Put Battery Terminals on Backward?

The failure of your engine to start should be the least of your worries if you put your battery terminals on backward. Reverse polarity can have more serious repercussions than this. Before listing some, let me tell you what reverse polarity is.

Reverse polarity is simply when your battery’s polarity is reversed because you’ve connected your positive terminal to where your negative terminal should be on the battery and vice versa.

It may sound like an open circuit without a flow of electricity, but believe me, there’s always electricity flowing out of battery terminals with reversed polarity. Reverse polarity also produces heat within the battery.

The scariest part is that the electricity and heat may cause hydrogen gas (which is highly ignitable) to blow up the battery casing. Don’t forget that this gas is always present in car batteries.

This may release sulfuric acid to the sensitive components of your vehicle, corroding and destroying them instantly. It may also cause a fire explosion, leading to an injury or death.

That’s why you want to resolve this issue as quickly as possible.

How Do You Fix a Reverse Polarity On a Battery?

The good news is that reverse polarity on a battery is quite easy to fix all by yourself without needing any special tools or advanced knowledge.

All you have to do is switch your wires’ terminals to their corresponding battery terminals. In other words, connect the wire with a positive terminal to the battery’s positive terminal and the other one with a negative terminal to its negative terminal.

N/B: Your engine comes by default with two types of wires for your battery. The positive wire and the negative one. The positive wire comes with a positive terminal which is red or marked by a positive(+) signal.

The negative wire, on the other hand, has a negative terminal that is black or identified with a negative(-) signal.


If your battery is hooked up backward, your engine won’t start simply because the start relay will not function, thanks to reverse polarity.

This component is designed to trigger other electrical processes, which occur when you turn the ignition key to start the engine, only when it receives power naturally.

The abnormal power that will be generated when reverse polarity occurs won’t trigger it hence the car won’t start. This can also be dangerous as it can cause the battery to explode, sending damaging acid to your delicate engine components. A fire explosion can also not be ruled out.

The good news is that you can resolve it by connecting your positive and negative cables to their corresponding terminals on the battery.

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