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battery drain

Flchallenger

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How do you test for this. I have a stereo system with 2 amps. I thought they may be the problem. Battery kept going dead only a year old so the swapped me out a new one and the same problem. So something must be draining the battery. Any suggestions on how to determine what it is. Other than disconnecting one thing at a time and wait several days and see if it is still charged. Also I saw under a posting about a fuel gauge can cause a battery drain. Is this true. This is a 71 challenger that has a new wiring har
 

70chall440

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I dont think it would be the fuel gauge. First thing to check is how your accessories are connected to your electrical system and whether or not anything is connected directly to the battery (like the constant connection of all aftermarket stereos for saving the channels and clock).

I will say this, all batteries will go dead over time usually especially anything in a car. I have battery tenders on everything I own for this reason. The only thing that doesn't kill the battery that I have is my 48 Ford 8N tractor, everything else will deplete the battery over time.

I am sure you will get some other responses about this issue but I chased something exactly like this in my 70 Challenger for years and could never find it (I am very experienced in electrical systems).

There is another option, a battery cut off which takes the battery completely out of the system, which actually reminds me. Have you tried disconnecting the battery and letting it sit to see if it degrades over time by itself?
 

Chryco Psycho

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The clock always draws power when sitting , aftermarket stereos also have a memory that will draw power also , when you touch a disconnected battery cable to the battery if there is a draw there will be a small spark as you connect it or you can connect a voltmeter across momentarily & see if the as any amps flowing but most multimeters do not have a setting high enough to measure constant flow between the battery & cable without damaging the meter .
 

MerlinsMopars

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Starter solenoids can go bad and draw power but still start the car. Disconnect the hot going down there. Also the blue wire coming out of the stereo turns the amps on and off. That may be another culprit, leaving the amps powered on.
 

Robert Franke

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Hello I am a retired dealership service tech with alot of experience on this subject especially since the cars got loaded up with control modules talking to each other..luckily our old stuff is super simple..First look up how to do a parasitic draw test..modern cars have up to 50 ma. Draw when off..avg 30ma. This will be ok in a car with the right battery for about 2 weeks. Our cars will have much less than that..First easy test is find a test light with a BULB..inside. Not LED! Key off..doors closed..every thing off. Disconnect neg battery cable and connect test light to cable. Touch neg. Battery post. If the BULB equiped test light lights up even dim..you've got enough to drain a battery. Now while you've got that glowing start pulling fuses..watch till light goes out..that will tell you witch circuit has a problem. Be sure to remove dome light door jamb switch while you have a door open! You dont want anything trying to work. If your aftermarket stereo equipment is wired correctly it shouldn't draw enough to cause your problem. The Right way to do the same is connect a Digital Volt ohm Meter between neg cable and battery. Set to DC milliamp scale set to Amps first! If you have enough draw it could blow the meter protection..just like You started with the Bulb test light if it lights! You're in the Amps scale! Big draw!..if the test light doesnt glow that's when you go to the DVOM. And go to MA scale. Gotta get below 30ma. Fuse removal will show you..Now if that doesnt turn bulb off..Go to your alternator. Disconnect it..I've seen some internal shorts in them..its rare but happens..I read one post about the starter..IDK. never seen that but it might be possible. Good luck! It's simple to do. Just remember to make sure EVERYTHING is off before testing.
 

flohemi

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Let me ask, how long does it take to drain your battery down to the point that it won't start. If you let the car sit for weeks at a time then a small draw is going to kill the battery sooner or later, if it dies in a couple of days after being fully charged then you have a problem. You can handle either situation with a battery disconnect switch that mounts on your battery cable but my choice is do not drive your self nuts trying to figure out what's drawing on your battery and install a battery tender, around $40 and they work great and will keep your battery at 100%
 

moparleo

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Before you start doing stuff lets get a little more specific on your issue. You say that you replaced your battery and it went dead again or low enough to not start.
Did you fully charge the battery before you got started or just assumed it was full charge. New doesn't always mean charged.
Next how long did it take to discharge. Hours, days, weeks ?
Post number #5 has a lot of good things to do. No magic, simple answer. You are going to have to do a search for the problem. You should probably have the stereo on a switched circuit so it only works with the ignition on. You are doing what a lot of newer guys do which is to load up the electrical system on a 40-50 year old car with a modern electrical item. Modern cars are pre wired for amps and stereos. Have higher amperage charging systems and modern wiring, connectors and computers that can help cope with these loads.
 

NoCar340

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Knowing a "goes dead" time frame would be a great help here.

Does your stereo work with the key off? If so, rewire it correctly. Even with the power switch off, most car stereos will draw more power via showing the clock or keeping the face lit than they would with the main power wire connected to 12V key-on. This is especially true of newer stereos with "soft start" (tactile) switches and ridiculous multicolor demo modes. Any digital car stereo has two 12V+ inputs: one is typically yellow for station/position memory and clock (if so equipped); the other is main power and is most-often red. The main power wire needs to go dead with the ignition key. If you want to listen to the stereo with the car off, there's an "Accessory" position on the ignition switch for exactly that reason.

'Twas a common repair to make way back in my installer days, along with Scotch-Lok/wire nut/twist-and-tape connections, speaker wires bodged into RCA inputs, and other common "I can do it myself" errors made by people who clearly couldn't.

If a parasitic load test results in a popped fuse in, or the destruction of, your DMM I would expect your battery to be dead every time you tried to start the car (unless you left the lights on during the test by accident). A drain greater than 10A will drop a car battery below starting capacity in a few hours. If the drain's that bad, you've got a major defect in your wiring or equipment.
 

Mastertech

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In the good old days when these cars were new we would take the shop AVR (analog not digital ), remove the negative cable from the battery and connect the voltmeter leads in series between the negative post and the negative battery cable. This acts as a milliammeter. You can use any analog voltage meter in this way. When you have a parasitic drain the needle will swing all the way to 12 volts. Normal acceptable losses may show a reading of about 2 volts. Pull fuses one at a time to identify the problem circuit. A shorted diode in the alternator is also a possibility. With an aftermarket audio system is the power to the amplifier or powered sub go off with the ignition switch or is it connected directly to the battery? You may need to install a relay to make sure there is no power supplied with key off.

As stated above the wiring in these cars is actually very simple. If you take it one step at a time it should not be difficult to find the offending circuit.

A memory just came back about a customers car that had the same problem way back in about 1980. Had me doing some head scratching when I noticed that the dome light was glowing just a little bit. You would never see it in the daylight but in the darker shop it was noticeable when you looked right at it. Disconnected the door jamb switches with no change. Same with the head light switch. At this point I started checking and pulling each of the fuses. I found that the clock fuse was blown, popped in a new one and be damned if the stupid light went out and no more drain on the battery. Electricity is always looking for a ground and if it can't find it in the normal way it can take the path of the next lowest resistance to get their.

Good hunting
 

Flchallenger

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Found the culprit. It was the one of the two stereo amplifiers was constantly on. I used the test light and started pulling the fuses. worked like a charm. Put the fuse back in and disconnect the power one at a time to the amps. Bingo.
 

Robert Franke

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Good Deal! Test light doesnt lie! Glad you found it. Its usually somthin added. Now if it sits for long periods a battery tender will keep it ready when you are.
 
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