Q: Is my aftermarket stereo draining my battery?

asked by on November 27, 2016

Hello,

Installed a new head unit (Boss) with harness but had to run red wires to the fuses to get to a switched circuit. Later battery dies and alternator light comes on so i bring it to a shop and they replace battery and alternator. I let the car sit for 4 days in 30 to 40 degree weather and the car wont turn over but turns over immediately with a jump pack. No lights are on and glove and trunk lights don't seem to be on. Don't have a multimeter but am getting one to confirm. I've heard this is common with aftermarket stereos...
My car has an automatic transmission.

A properly installed system should not drain your battery in 4 days. Obviously, the simplest way to rule it out would be to disconnect the stereo for a few days and see if that remedies your problem. If it does, you will need get your hands on an inductive ammeter that can read milliamps. You can clamp the probe around individual wires to see what the draw is on that particular line. There should not be more than 200 milliamps total draw when the car is shut off. But here’s where it gets more complicated. Your car’s body computer may be active for up to 20 minutes after you turn everything off, so the draw will be higher until the body computer "goes to sleep". That means it can be tricky to measure the shutoff current.Also, if your stereo is hooked into a line that is shared by the body computer, the computer may interpret it as activity, so it might not go to sleep properly. If all this sounds complicated, that’s because it is, but by contacting Your Mechanic you can have a qualified technician come to your home or office and check out your electrical drain and tell you what can be done about it.

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