Hey Everybody!

New proud owner of a '93 240 Classic Wagon here, making my first post on the forum, and desperately seeking advice. I have ran into some very strange electrical issues with the car, and being only 22 years old and very unexperienced with the electrical functions of a car, I could really use some insight. I bought the one-owner, 104k miles wagon about a month ago, and it held up quite well for the first couple weeks. Then, I began encountering battery drain issues - there were a couple of instances where I accidentally left an interior light on for no more than 30-60 minutes, and the battery went completely dead (down to about 10% charge, no clicks in turning the ignition). I'd proceed to get a jumpstart, and the alternator would then charge up the battery, no problem.

After this had happened a few times and before I had a chance to try to do anything about it, I then replaced the non-functional stock radio with a Kenwood receiver & new speakers. This painstaking endeavor took place about five days ago. In the process, fuses 4 and 8 were blown, and have since been replaced. The proper wiring harness was used, and I connected red to red for power to the stereo, and yellow to yellow for constant 12 V to the stereo to allow settings to be saved, clock functions, etc. The stock amplifier has been bypassed using the necessary wiring harness.

Since installing the Kenwood receiver, the battery can no longer hold a charge. If I simply turn the ignition such to allow the stereo to play without the car on for ~30 seconds, the battery will drain completely from >75% charge down to 10%. If I even turn on an interior light, the battery will instantly drain to 10%, not even a click when i try to start the car. What's more, if I don't do any of that and simply leave the car sitting overnight after restoring it to a full charge, the battery is completely dead the next morning, just from the stereo being plugged in (12 V constant power being ran to it). The other night I checked the battery and found it to be at 85% charge, didn't even open a door after checking it, then the next morning it was at 10%. I understand that this means there is likely a mistake in my wiring causing a short, but I don't know what the mistake could possibly be. I followed all instructions from a variety of sources on how the wiring is done, and I am relatively familiar with stereo wiring in general and have done it before. I am truly at a loss on this one.

What I've done in response to this to keep the car operational is simply disconnect the stereo harness from the stereo while I wait to take the car in to my mechanic (have to wait another six days, am doing it as a last resort unless i can solve it myself). This allows the battery to hold its charge, and the car will start as long as no light has been turned on, or anything else involved in fuse 8 has been engaged. If a light has been turned on for more than a few minutes then it still drains the battery completely, which I believe tells me that the battery is now bad. Otherwise, it holds its charge and the car starts when the stereo harness is not plugged into the back of the stereo.

I believe that at the very least I'm going to need a new battery here. Before I install that, however, I'd like to figure out what's going on with this instant near-full charge to 10% charge drop is all about. Regardless of a possible short, the 12 V constant power to the stereo certainly should not be draining a battery overnight. Anyone have any ideas?!

 

first of all put a meter on the battery terminals and see if the alternator is putting out at least 13.8 volts at idle. if that checks ok then do a load test on the battery. that should tell you a lot about the condition of the battery since the starter is probably the biggest consumer of power in the car...

 

Sounds like the battery is bad, the alternator is doing its job...
I'd change the battery, see what happens. The battery is most likely the problem.

 

Just did that. Alternator is a bit weak.. Was right around 13.7 V. Battery has been failing the load tests miserably, though. Could watch the voltage dropping quickly at the battery when the driver lights were on without the car on. Think i'm gonna go ahead and just replace the battery and see what that does

 

Sounds like a weak battery. The battery in my mom's car never failed to start, albeit cranking slowly, until I left the headlights on for a minute.

 

13.7 is fine, and apparently the alternator is doing its job, so don't worry about it--get a good battery, go from there!

 

Looks like the new battery has fixed my issues. Also discovered that there was an accidentally grounded speaker wire that was likely draining the old battery over night, or shorting out the circuit. All is well now. Thanks for the help, everyone!