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ok a little history, about 6 months ago my battery light came on but nothing happened, still drives fine, alternator appears to be ok, don't know why that came on. Anyways, so when it started getting cold here my radio all the sudden turned off along with my XM unit, simultaneously, then about a second later both powered back up. However this is started to happen more and more and now when I drive down the street it turns off and on again the whole time I am driving until I stop. But the car has nothing else electrically that is turning off just the head until and XM unit. Any ideas??

 
Rep Power: 786

could very well be a bad ground but I would say probably low voltage. different electronics will react different to lack of voltage, and I have experienced my head unit shutting down due to lack of voltage, although not with my civic. If you have access to a digital multimeter, get a reading while you are driving and if it is low (like 11 volts or lower) consider getting your battery and alternator tested and possibly replaced.

 
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As MegaHurtz said, some electronics are more sensitive to voltage changes than others. Typically, stereo decks (and anything connected to them) are very picky about input voltages. You can take your battery and alternator out and have a free test at AutoZone, O'Reilly's Auto, or whatever is around you to eliminate those as problems. Another option is to check the wiring behind your deck to make sure the connections are not coming loose.

Is your car throwing a check engine light code? There are a few that relate to the charging/electrical system. Have any fuses blown?

 
Rep Power: 322

are you running any amps?

 
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yeah I got an amp but I have been running the same set up for over 2 years now with no problem until now. I have an optima yellow top so the battery is good for sure. I would imagine the alt is still good being as how the battery has never drained down. Well the weird thing is that it doesn't do it everytime. I just drove around for about 10 mins and no problem. But this morning the same drive it cut off and on about 7-8 times.

 
Rep Power: 786

don't just assume that becasue you have an optima yellow top that the battery is good for sure. do you want to exhaust all other possibilities and then look like a fool when it turns out the battery was the problem the whole time?

sounds like a voltage problem, go get your electrical system tested.

 
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so I should get the battery and alt tested at oreily's and then where should I look? I dont have a DMM though so I can't test anything on my own.

 
Rep Power: 261

go to autozone the DMMs there are cheap plus its a godd investment, auto, home and everything wise

 
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ok so if I have a DMM what do I test and what numbers do I need to get

 
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sounds like you should get a new car battery