Q: Electrical - car battery positive temporarily touched negative - where is the problem?

asked by on February 02, 2017

2009 Mazda 6 4 cylinder Keyless ignition

When I was installing a new battery I accidentally touched the negative and positive cables to the wrong terminals for a second. The car horn sounded and it sparked. I quickly pulled the cables off and put them on the correct terminals. Now the car will not start, no lights, nothing. I Checked the battery and it is measuring 12.6 volts. I pulled the cover off the engine fuse box and noticed the main 125 amp fuse was blown. I disconnected the battery and installed a new 125 amp fuse. I reconnected the battery. Now the brake lights work and the horn works. However still no interior lights, radio, no sign of life on the inside. Also the front lights do not. I looked at the other fuses in the engine fuse box and the inside fuse box and they all appear fine. Is there another fuse outside of these areas that could be blown or something else I am missing?

My car has 50000 miles.
My car has an automatic transmission.

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Reverse polarity, at the battery, in a 12 volt electrical system on a car can cause a variety of effects including damaging the alternator, diodes and the numerous microprocessors on a vehicle such as those in the powertrain control module (PCM). As far as other fuses, they are numerous not to mention fusible links, circuit breakers, and all of the individual electronic components themselves in many circuits that could have failed due to to reverse polarity. Inasmuch as the vehicle does not start, the simplest thing to do is diagnose the starting circuit first as, in the course of that, other fundamental failures (for example if the PCM was fried) will come into view. If you want these steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request an electrical diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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