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I bought a 2012 Hyundai Accent and when I went to pick it up the previous owner said "We will have to jump start it, because it has been sitting for a month". She insisted on using her cables so I connected them from both cars battery terminals. They started getting hot and the Hyundai still didn't start. I grabbed one of the clamps and it burned my thumb, but I got it off. The battery should have been fine because it was only a month since it was last started. This is when she told me the car had a remote start and a kill switch so evven after you unlock the door, get in, and insert the key in the ignition, you have to push the door unlock button on the fob before you turn the key or it won't start. I looked at the cables on the ground and there was a cut in the middle of them where positive and negative cables were in contact with each other. I got in the car and now knowing about the kill switch it started right up without jumpers. The only damage from this idiotic episode is the stock radio/CD player blew it's 20 amp fuse. I replaced the fuse with the correct 20 ammp fuse and I saw it blow as soon as I pushed it in. I took the radio out and took it apart but nothing looked burnt and the only wires inside are those ribbon type wires. I located the live wire and the ground wire at the plug that goes into the back of the radio and touched them with my multi tester and they showed 15.3 volts. That's about as much as I know about car electronics. I also tested the AUX to the ground and got the same voltage. Any other diagnostics you could recommend would be appreciated. I took all the tape off the two harnesses that go to the radio and didn't see any melted wires.

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  • Welcome to Motor Vehicle Maintenance & Repair! Dec 4, 2023 at 11:03
  • If everything else is working correctly and the fuse continues to blow, I'd suggest this was a pre-existing condition which was undisclosed by the seller. I'd be looking to rewire the head unit to ensure it is correct. 15.3vdc is quite high for voltage through the system. Normally, 14.5vdc is the max I'd expect to see with ~13.5vdc being about normal for most vehicles with the engine running. I'd check the voltage at the alternator to see what the voltage output there is to make sure. Dec 4, 2023 at 11:07
  • I thought 15.3 vdc was high too. I had a Volvo C70 and when it was running, the battery read 13.5 volts. And the Volvo had power everything. The radio was working though before the attempted jump start. I connected the cables to the battery posts instead of connecting the ground to something else. The radio has a large screen that tells the time and such whenever the car is running. I already stripped the two harnesses that go to the radio as far as I could. I guess I'll have to dig around under the dash so I can see the whole harness. Dec 5, 2023 at 18:48
  • At 15.3vdc, I'd expect the system to boil the battery at some point. Dec 5, 2023 at 20:36

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The battery jumping procedure wouldn't cause the radio problem; The batteries are a maximum of somewhere around 14.5 volts when the alternator is running. But if there was a short circuit, it would be less, never more. The worst that can happen with the short circuit is the battery could explode, or the cables could burn. It would not affect the car itself, just the battery.

The reason it's not good to connect the lead directly to the battery for the final connection is only because there could possibly be some gas released from the battery, and when you connect the lead, it could make a spark right at the battery, causing an explosion or other anomaly. So, connecting the negative lead to the chassis is far enough away from the battery so the gas would not be concentrated enough to ignite. If it didn't do this, then there is no problem.

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