Electrical: HEEEELLLLLLLP!

[Mike Hausner]

I know this isn't COBRA related but I would appreciate any help from you guys.

Here's the situation:
I offered to help fix my sister-in-laws car. Since she hasen't got a pot to pi$$ in and I have some time on my hands (layoff 12-'03), I volunteered.

The Problem:
The battery keeps going dead when the car sits overnight so something has a short in it. I have disconnected the alternator and still read battery voltage and 10ma drain between the disconnected neg cable and the neg battery post. I tried pulling fuses one-at-a-time and I still get a drain in the battery.

So, how do I go about finding the circuit that has the short?

As a stop-gap measure I installed a post mounted battery disconect switch and instructed her on it's use.
BTW the car is an old Dodge Caravan, 4-cyl, non turbo

Thanks for the help

[trularin]

10 mA is normal draw for a car with a clock, cluster (with class 2 or better communications ), interior lights independent of the ignition and any other assortment of connected peripherals that go directly to the battery.

May I suggest you do a load test on the battery and see if it can hold a charge?

If it passes the load charge, check the charging current ( clamp probe should work ) and charging voltage.

Hey, it's just a thought.

[Ron61]

Trularin is correct about the drain not being excessive if she has a clock or anything else that is hot at all times. Battery could just be so low in capacity that it will not hold a charge unless running. The load test is the easiest way to check that. If the battery shows ok, then make sure the alternator is putting out a full charge when it is running.

Ron

[Cal Metal]

If the battery checks out, you might want to check for a bad diode in the alternator.

[trularin]

Good call Cal Metal.

Start the car and pull the battery connection. If the charging circuit it working, the car should stay running. Check the voltage across the terminals that would be connected to the battery.

14V +/- .5V will work. However, the alternator may read this as a dead battery and run the voltage up to as much as 15.8V.

If it reads erratic or low, could be a diode as Cal Metal suggested.

Hope this helps.

[Excaliber]

Eliminate the alternator 100% by disconnecting the main battery wire as well as the other smaller wires attached to it.

I to have found a slight drain on the battery measured as you indicated could well be considered "normal".

The key comment leads me to believe that putting in the isolation switch has solved the problem. If so, then indeed there is enough drain on the battery to draw it down overnight?

Pulling the fuses did not seem to help. Next thing I would do then is disconnect the main firewall to fuse block connection in the engine compartment. If it STILL drains down the problem is under the hood, not INSIDE the Van.

Do try to replace the battery with a loaner or some kind, at least for test purposes. I'm assuming you don't have the money or expertise to have your existing battery verified.

Ernie

[Mike Hausner]

Thanks everyone for the responses.

The alternator checks out OK and it is charging the system fine.
I tried completely disconecting the alt and still had a drain on the bat.

The battery is only a month old and if I disconnect the (neg) terminal I can watch the battery slowly coming back up on the voltmeter. It's only if you leave it for a couple of days that the bat drops below 10 volts. Not sure how many amps is being drawn.... 0.01 is what the VOM said.

I'll try the main connection to the fuse block.

How does one go about checking the individual circuits? Continuity to ground with the bat disconnected?

How should I check the positive cable? I think that goes directly to the starter. I'd like to check it. Could it be grounding somewhere?

I'm not good at troubleshooting electrical systems and I even had a couple of MGs to get experience on. LOL

Thanks for any more suggestions.
Mike

[Ron61]

Mike,

As Ernie said above, see if you can isolate the drain to under the hood or inside the car. Sometimes these things can be a real pain to find. If you want to see if the Positive cable is a problem, just disconnect it and then touch your Negative cable back and see if you get any spark or current flow. If you can get an area to look in it will be much easier. If you can find someone with the same wiring set up that you have that will make it much easier as they will know exactly which wire goes where. I spent a year trying to track down a similar thing on my 69 Ford Torino Cobra and finally isolated it to the darn fuel tank sender unit. After looking at all the work it was to just get the tank out to fix or replace the sender, it is a NASCAR type setup, I went to NAPA and bought a $29.95 battery tender and I just hook that on and I never have had a low battery since. In fact it worked so well that I got another one and use it on the replica as it sets so long during the Winter. They are small and will mount right by the battery.

Ron

Ron

[rdorman]

I just went through the same thing. Everything tested out fine. Ran the full set of diagnostics. Even had the battery tested. No issue. Took the battery back to some one who knew what the heck was going on for testing, bad battery. They can be bad right off the shelf. Some of the places have some pretty darn advanced testers these days. The one at Autozone ran it through a whole list of timed tests. Not just a simple load test.
Rick

[REDSC400]

Another thought....

Some cars have "Automatic" driving light and headlight sensors. These sensors are a photo-voltemic electric eye that consumes a little bit more power than you would imagine. If the headlight switch is in the A or Automatic mode then, you could get substantial power draw during the evening. Usually the sensor is on the dashboard near the window.

If this car has one, you may want to put a dark rag over the sensor (to simulate nightime) and see if the power draw increases.

Sadly, I learned this factoid, when on a business trip, I left the setting in Auto on the Lexus and came back after 2 weeks to a dead battery. The owner's manual suggests turning this switch from Auto to Off if leaving the car for a long time....

Hard lesson learned...

If the car does not have one of these... Then forget Bout It.

[mr0077]

Also, just to build on/clarify Cal Metal's diode thought, check to see if there is a change in amperage draw when you connect/disconnect the main power wire at the alternator (with the motor and key off)...if no diode problems, there shouldn't be any change with it on or off of the terminal.

[Trueoo7]

Had a friend who has a C4 vette and he had to replace his battery. Since he was using the side terminals only, he decided to cut the top positive post off flush since it was sooo close to a metal bracket on the car. Took us forever to figure out that the top post is what feeds the side posts and the top post is actually a post within a post so with the ever so slight seperation between the two we couldn't get the car to do much of anything that required a big draw, liking starting the engine. Everytime we checked the battery it read 13.5 volts. Scratched our heads for a few hours to say the least. Ruined a brand new battery too.

[slithering]

Mike,

If you still have a problem, Pull your positive off the battery post. Pull your fuses one at a time and put an ohm meter across the two points of the fuse receptacle. You should not get a reading. If you do, determine the fuse and wire color and find it's next connection point. If it splits, do the same test again until you complete the circuit. If you can't find it, send me a private message and we'll hook up over the phone.

Chris-
slithering

[wilf leek]

ummm - just my 2cs, but a 10 milli-amp (that's ten one-thousands of an Amp) draw should not flatten a car battery for some time. Weeks probably. Most car alarms draw more than that and they are usually OK for 2 weeks or more with a healthy battery, or airport carparks would have lot more auto rescue men in them than I usually see.

Could you double check that amperage draw reading? Of course, you still have to find out what it is that is drawing it.

[John Poling]

Mike,

Haven't seen this asked yet. What year is the van?

John

[Mike Hausner]

The Caravan is an '89.

I think the amp draw is more like 100ma (dam decimal point...where did it go?) With the battery connected you can watch the voltage drop.

The bat disconnect switch is a temporary solution. I want to find the problem before it gets any worse.

Slithering, I'll try the fuse thing as you stated, probably this weekend. She lives in the next town so I'll have her bring the car to my "shop" instead of working in the parking lot.

Thanks again all for the help!
Is this a great family or what!

[John Poling]

Mike,

In the mid '80's Chrysler cars had a problem from time to time with the switch that controls the rear window defogger grid. There appeared to be some kind of internal to the switch malfunction that allowed a current drain through that circuit. If I remember correctly, the LED light on the switch would actually stay lit. My Mon had an 86 New Yorker that had this very problem you are describing and that was what it was on her car.

Does her van have a rear defogger grid? Check it out, also look for other switches that have the light on it that may control other items.

John

[Mike Hausner]

Thanks for the tip John, she's going to bring the car over Saturday. Looks like I got my work cut out for me.
If & when I find the problem I'll post the fix on this thread.
Thanks All!