: Parasitic Drain...how to?

06-15-11, 10:07 AM

So I've replaced the battery, alternator, voltage regulator, and battery cables in my 69 Caddy due to battery charging problems.

Somehow I must have shorted something out or messed up somewhere because the alternator appears to be charging the battery properly (12V with the car off, between 14 and 15 when the car is running.) but if I leave the battery hooked up it drains over night.

What is the best way to test for parasitic drain? I have two multimeters that can test voltage, amperage, resistance, etc...I do not have, nor could I find, one of those parasitic test things that go on the battery terminal...is there a way to check this with a multimeter?

Also what is the best way to track down the cause? Could a poor ground cause this problem? I ask this because when I was connecting my negative battery cable to the ground i noticed that the bolt that holds it doesn't get super tight. I was thinking about replacing it with a normal nut/bolt combo instead of the bolt that is in there now, which is like a self-tapping screw type thing.

06-15-11, 10:21 AM
From what I've learned, you hook up the multimeter to the battery to read voltage(I believe) and you should see it dropping slowly. Then you start pulling fuses one at a time until the voltage stops dropping. Whatever fuse is pulled that stops the voltage from dropping is the related to your problem. So if you pull the power window fuse and the voltage stops dropping, your drainage is in the window circuit. A bad ground would cause a weak battery but it would drain it.

06-15-11, 04:08 PM
In addition to chasing down the electrical drain... You may also consider adding one of those negative terminal quick disconnects so you can quickly disconnect the battery during longer periods of inactivity. I know the mechanical clock in my car is constantly feeding off the battery, not much, but its running. If I know my car is going to sit there for over a week, I usually disconnect to reduce wear and tear on the clock, battery, etc.

06-15-11, 05:09 PM
What csbuckn says is the usual way to chase the problem.

I think something similar happens to my 69 and thatīs why someone time ago went crazy:woohoo: disconnecting every electric connection and stretching new wires with different relays. Now Iīm still finding some device disconnected. At first, after leaving the car in the parking space for 2-3 days, I found that it had no battery at all. Consequently, I always disconnect battery when the car is going to be more than 6-10 hours parked. Doing that Iīve never had any problem. Maybe some day, when everything else is fixed, I try to locate the problem. Anyway, itīs not easy in most cases.

06-15-11, 06:53 PM
So in the factor service manual it says hook a voltmeter between the + cable and the + post of the battery and it should read 0 volts??
Mine reads 12 volts...

Maybe i read it wrong and it wasn't asking for volts but amps. not sure. Also I noticed that when I shut my car off the battery has around 12.8, 12.9 volts but it quickly starts dropping. Is that normal? Or is the battery being overcharged?

06-15-11, 07:17 PM
All of that is normal except the drain after you turn the car off. Not sure why the book says it should be at 0. So you just have to pull fuses one at a time with the car off to find out which one stops the draw. Is the anything in the car that's not acting right? That would be the fuse to start with.

06-15-11, 07:20 PM
radio doesn't turn on at all but it's not the original radio. I will start pulling fuses! Thanks

06-15-11, 09:10 PM
Use the ammeter inline between the negative battery post (use vise-grips or similar) and negative battery terminal. On newer cars we'd recommend that you don't break the connection while connecting the ammeter (use a jumper wire -- requires a 3rd arm), but something this old shouldn't have any fancy electronics. You should have no more than 0.050 A or 50 mA (milli-amps). Once the ammeter is hooked up, start by disconnecting the alternator, go read the ammeter, then the fuses one by one, check the ammeter, etc... until you narrow the circuit down. If the battery dies over 3 days I suspect you have a draw of about 1.5 amps (1500 mA).

I had a Grand Marquis that had the same problem years ago, disconnected every fuse and still had the draw...rested my hand on the alternator to scratch my head and got burned. The diode pack in the alternator shorted out and wiped the battery dead in no time. It too would charge while running, the alternator had to fight itself, but once the engine was off, the failed diode won.

Had a 77 CDV with an inoperative horn. The horn pad stuck, burned out the horns. The relay never quit though. It stayed pulled in and kept killing batteries. I was 16 and it took me months to finally track that down...all these years later the same thing happened on my 84 Fleetwood, no horns, noticed an occasional click when I'd hit the horn pad ever so slightly. That one was intermittent, but with 2 batteries, it never ran them down (Diesel). Had to take the horn pad apart and repair it, and replace the horns. Man, did they stink like burning once I got them out.

06-15-11, 11:04 PM
thanks for the info tqwrench. I just put a new alternator on the beast so hopefully that is not the problem. I will have a look at it and find out.

06-16-11, 01:37 AM
Start with that replacement radio and look for other wiring that has been altered over time while you are at it. Some people say that the clock can also cause problems if it's not working right so you might want to try disconnecting that too and see if it makes a difference.

06-16-11, 08:18 PM
i think i may have found the problem...pulled the fuse for the heater and the drain appears to have stopped. I will find out in the morning for sure. hehe

06-17-11, 08:53 AM
Negative on finding the culprit. It appears I slowed the drain but it's still draining. Let it sit over night and came out this morning to find it at about 3 volts :(

06-17-11, 08:58 AM
Maybe itīs a combination of elements. Keep this fuse out and go on checking fuses or other elements. As tqwrench has told, it could be the most stupid device :) In my 69 fan was disconnected too. It seems someone was in despair in the past looking for the drain. When we connected it again it did no great difference as the battery kept charged when connected for 12 hours.

06-18-11, 09:18 AM
Update: I finally found the drain! for real!

I pulled the circuit breaker for the horn, and also pulled the fuse directly across from it...the uh...clock, lighter, body fuse. With both of those out the amp drain went down to 0 and the "engine temp + buzzer" key in ignition warning no longer comes on. I'm thinking it's due to that stupid warning thing. If you remember, it was always on, even when the car was started or the keys were out. Any time that door was opened it would come on.

Now I will just need to find the problem and fix it :)

Thanks for all the help, guys

06-20-11, 12:59 PM
hey Matt
pm'd you a bunch of times and didnt hear back
did you get them?....Jim

06-20-11, 01:34 PM
Jim I haven't got any but I did get a message saying my inbox was full. Shoot me an email, it might be easier.