car battery wrong connection

By YOUCANIC on Apr 1, 2019

Jump Started or Installed Battery the wrong way

Car owners may accidentally connect the jumper cables in reverse order or install the battery backward. The vehicle may no longer start. The purpose of this troubleshooting guide is to help answer the following questions:

  • Hooked battery up backward now car won't start
  • What happens when you connect a car battery the wrong way
  • Car battery connected backward 
  • Car battery installed incorrectly
  • What happens if you hook up battery cables wrong
  • Accidentally installed car battery in reverse
  • Hooking up battery cables backward
  • Hooked battery up backward on four wheeler

Connecting the jumper cables backward or installing a new battery the wrong way is never fun. In this article, you will find troubleshooting steps that will help you diagnose such problems. 

Installed new battery backward, car won't start

You decided to change the car battery but accidentally put the cables backward. Instead of connecting the positive (+) cable to the positive battery terminal, and negative (-) cable to the negative battery terminal you hooked them up backward.

 All of the sudden you see a scary spark and your car goes completely dead.  Car will no longer start. Dashboard lights are off, and everything is dead. Key may not even turn the ignition. Similar symptoms will be experienced when you try to jump start a dead battery but you accidentally connect the jumper cables backward. 

car battery short wrong connection

When a car battery is connected backward a fuse designed to protect vehicle electronics should blow. If your vehicle doesn't have a fuse (almost all cars do) designed for this purpose, you will send electrical current backward through systems in your car including ECU, transmission control unit and more. If current flows backward through lights that's not a problem. The issue is when current flows backward through an electronics that have diodes such as the ECU / ECM (Engine Control Unit / Module).

It is not common to damage the Engine Control Unit / Module by connecting the battery cables incorrectly. Most of them are designed to withstand reverse polarity. In the worst case, the ECU/ECM can be removed and inspected if a diode has failed. 

Troubleshooting Car Won't Start Problem

Step 1

Check the high ampere fuses on your car. Most vehicles have a large fuse that will blow and avoid damage to the ECU / ECM. This may be a 40, 60, 80-ampere fuse and it is usually hard to find. Here is a picture of this fuse on a Honda Civic. When the jumper cables were connected backward, this fuse blew. This is from a 2015 Honda Civic. 


Car?battery backward?damageNotice the fuse strip. More than one fuses can blow. Once you replace this fuse, start up the car. In most cases, the car should start right up. If it doesn't, continue to Step 2. 

Step 2

After you replace the blown fuse, you may still have a problem starting the engine. The engine may turn over and crank, but it will not start. Now it is time to check all the smaller fuses. Make sure that the fuse for the ignition system, ECU, fuel pump, Immobilizer are still good. What happens when you connect a car?battery backward

Step 3

If all the fuses are still good and your car still refuses to start here are a few things you need to check. 

The car turns over but won't start. 

  • Check if there is spark at the plugs
  • Check fuel pressure
  • Check if direct injectors are getting power

Car won't turn over or crank. 

  • Immobilizer system
  • Engine Control Unit is getting power
  • Check to see if the starter is getting power

Step 4

Hopefully, you were able to diagnose the problem yourself. If you are still having problems with being able to start the car you may want to consider having a mechanic take a look at your car. Avoid letting water or rainfall on your fuse panel. 

Car?battery?installed incorrectly

Do not allow water or rain on your fuse panel. 


Nate, 2019-02-01

Put my battery cables wrong now my car won't start so do I have to check the fuses in the ignition switch I have a Dodge 2008 caliber I accidentally put the negative to positive and now my car won't start I have lights on inside the car in my radio on but I don't hit no crank crank noise so what should I do

Trishia, 2019-02-03

Hooked he batter backwards got everything working then 2 days later the car would tu3n over but won't start

Julian , 2019-02-05

I have a2010 Malibu and I put in the battery the wrong way cranks but won’t start

James, 2019-02-06

Hooked up a new battery backward and now car won't start on a used Mazda Millenia 2000; opened up the fuse panel to find out that a previous owner had removed the main 120a main fuse and bypassed it. Now trying to figure out how to proceed.

I have a 1968 Corvette 327 and my son put the battery in backwards put the charger on it and walked away.  Came back 20 minutes later to a cloud of smoke coming from the battery.  Can you help me figure out how much damage he did and where I would even start to look.


ChaseQuinn, 2019-04-11

The battery is gone for sure. The acid in the battery is contaminated at the very least. Check your ECM, starter, and fuses. That is the most common issues.

J@Y, 2019-03-07

I just had my jeep patriot battery die while at sons soccer practice. Got a jumper cable but connected to wrong terminals. Car then started up after changing terminals. However. Now my interior lights will not turn off even when I hit switches. They stay on. I removed fuse. And they still stayed on. Any help??

Matt, 2019-03-14

Battery wrong and now I have no power whatsoever before I hooked it up wrong it was just a clicking and sometimes nothing when battery was dead but the clicking made me think starter should I replace put a brand new starter on vomiting starter on we switch batteries in my dad's truck to my truck and somehow it got backwards and that's when the battery cables were switched just for a short time then taking off and swap back over now I have nothing no power no lights no nothing.

John Petree, 2019-03-30

So they all say want start u did this same dumb thing today trying hurry in rain but only thing Is my car still runs alit of smoke came out a and sounded bad it blew my radio fuse but that's all why only that and is it ok then what else should I check I not the best with cars just know the basic

Kevinpb213 , 2019-04-17

Any idea what happens when you ( me) hook up a battery backwards on a Yamaha outboard . Boy do I feel stupid !!

Theresa Nepinak , 2019-07-24

Husband hooked up battery wrong way.

Noel, 2019-06-16

Have a Mitsubishi Montero sport 2015 model. got the battery connection backwards, saw a spark. I replaced the battery with the correct polarity orientation. engine started but everything inside the car is not functioning (head unit,gps, aircon, alarm, locks, sunroof, lights) what could be the problem?

Krissy, 2019-06-27

That happened to my 03 Nissan maxima and it was a fuse directly controlling those devices.

Thor, 2019-08-27

My Montero Sports have also the same problem, battery was hook backwards and now the Aircon, Head Unit, central.lock ang alarm are not functioning (no power). Im just curious if you you problem have been solve? Thanks

Marcus Felix, 2019-06-24

I put a new battery in backwards in my 2005 Honda and the parklights came on and the accident was buzzing but wouldn't crank. I realize the cables were backwards and changed them but now the car is getting no power. Not even the light or blinkers work. Need advice please. I checked the smaller fuses and there good but can't check sensors.

Corey, 2019-08-06

Could the backward battery blow the ac and radio

Lanette Ray, 2019-08-08

My husband hooked the battery up backwards on my honda civic ex ..changed it ..but now my car won't start dash lights or connection whatsoever

Shoronda, 2019-09-23

I. Hooked up my battery backwards. I didn't no my battery was hooked backwards. I was in a hurry it was raining. When I got to the store I smelled smoke not noting what to do I hooked another battery to it and drove home it quit when I got to the drive way.

Brian Bell, 2019-10-29

New battery hooked up backwards. Battery fuse blew in fuse box located behind battery. $8 at Acura dealership for 05 TL. Replaced and started right up.

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