Hey, new to the forums. Been doing a lot of research of my issue and haven't found any good information with a detailed explanation.

Okay, so I got a used '94 Civic from my Dad for Xmas this past year, he's had it since I was born and he's put all 414xxx miles on it himself. Well, recently when I got my tax return I decided that I was going to upgrade the stock radio in it, he had an aftermarket JVC deck in it previously but he got the radio as a gift and wanted to keep using it so he swapped the original back in.

Well, went to a professional audio installer, bought a radio and they installed it on a Friday afternoon, the Sunday after I started to get electrical issues.

It started out with my lights dimming really bad under load, but what really made the issue apparent was the erradic idle that my engine had and my tach and my speedometer would just drop when I kicked my clutch in. Eventually car died while driving. Got jumped and drove my poor baby home, luckily I was only a couple blocks from my house. Well, the power issues escladed, I figured it was just a dead battery from the extreme cold, when I got home I let it run with all the accessories off to charge the battery. Thought I'd be fine to run to the gas station to grab a drink and drive right back, turns out I was wrong, got jumped 4 times at the gas station and the car kept dying and at some point though all the jumpings the radio stopped working and the clock on my dash stopped too, so I parked it for the night.

So next day, came back to the gas station, removed my battery and took it to O'reilly's, they said the battery didn't show as bad, although voltage was too low to tell, they charged it for 30 or so mins, checked it and said it was fine. So took the battery back, hooked it up and the Civic started just fine, radio still not working along with clock though. Drove over to O'reilly's again, did an alternator test and the guy said my alt. was bad. Okay, figured that makes sense but why was my radio and clock not working and my idle irregular? Well, did some more testing, found a fuse in the engine cavity labeled "backup" and the fuse was not putting out full volts, swapped to new fuse and clock and radio now work. Also with recharged batt. idle isn't as irregular but when I go back to idle it fluxuates between 700 and 1300ish RPM, weird... still working on that. Anyways, now down to the real issue. When I turn the car off the battery light comes ON and stays ON. Like, key out, engine off, car locked, the battery light is still on. When I start the car the battery light disappears though. I've read a little here and there and the only answer I've gotten from people is there is either a short somewhere or it's a low battery indicator.

Assuming the alt. is bad then my car is running off of batt. only and since O'reilly's only charged the battery for 30 mins it is to be assumed the battery isn't at full charge, I haven't gotten to fully charge yet, considering I'm writing this at work but after I'm planning on charging the battery and seeing if the light stops.

I'm just confused, because I would think the low battery light wouldn't be on if the car is off, I mean it's just logical, if battery is low why would we leave a light on that is only going to consume more power?

Not sure, cars aren't my specialty... I generally work on computers but I professionally troubleshoot things all day so I figure with some research automotive issues shouldn't be much more difficult?

I know enough to be dangerous so please be clear guys!

I hope someone can give me an affirmative answer to why that light is on, it's the only issue I haven't figured out yet!

Thanks

 

A few interesting things:
The battery light is controlled by the alternator. It doesn't directly indicate the status of the battery. It is supposed to come on in some cases of alternator failure.
The "BACK UP" fuse powers the radio, clock, and part of the engine computer.

Start by pulling the BACK UP fuse with the key off, if the battery light goes out you probably have some crossed wires behind the radio, i.e. a bad install.

With the key on but engine not running, the battery light should come on. Then it should turn off when the engine is started. If it doesn't work that way, likely the alternator is bad. The light should never come on with the key off. Make sure that other systems of the car like the wipers and turn signals also stop working with the key off. The brake lights and the headlights do normally work with the key off.

Unplugging the 4 wire plug from the back of the alternator (do this only while the key is off) should make the light stay out at all times.

With the engine running but everything else off you should measure about 14 volts at the battery. If it is less than 13 volts the alternator is not charging the battery. This will cause the battery to run down and various systems on the car to stop working due to low voltage. Often this problem is the alternator itself but it could also be the big alternator fuse blown (this fuse is in the same box as the BACK UP fuse).

 

Okay. The battery light is on with engine off and the key removed from the ignition. Last night my battery light was on all night. Today, when I got in my car the battery was so low the vehicle wouldn't start. Now, the BACK UP fuse that was mentioned was replaced yesterday with a new fuse and the clock and radio started working. After the fuse swap the light was still on.

UPDATE AS OF NOW: I'm pretty aware that the alternator is dead, going to replace that ASAP Also, radio is removed and the harness used was removed as well, so the entire radio installation has been removed now. The battery light is still on with the radio removed and the car off with the key removed. I've taken the battery out and I have it on a charger charging now. Will see if a fully charged battery will knock that light off.

 

Unplug the plug with 4 small wires from the back of the alternator, light should go out. This is probably a bad alternator but it is an unusual symptom.

Again, the light comes on for one reason-- to indicate that the alternator has detected itself failing a self-test. It doesn't respond to the charge state of the battery.