[FIXED] Parasitic Battery Drain

I'm helping a friend with a 2003 Buick Century.

2 different multimeters show a .56 amp parasitic drain (after waiting). He just put in a new alternator but disconnecting all the wires on it had no effect. (I was thinking maybe it had a shorted diode, but no.) We pulled the fuses in the under hood fuse box one at a time. No change. We pulled the fuses on the side of the instrument panel one at a time. No change.

Here's the thing. It was something like 17 degrees yesterday and I haven't been in the cold a lot this year. So either I missed a fuse (or he wasn't watching the meter per instruction) or there is something that doesn't run through either fuse box that's pulling 560 milliamps. We're going to do this again tomorrow when it should be much warmer. But I keep thinking it has to be us. There shouldn't be anything on that car that bypasses both fuse boxes, right?

And, is there anywhere to just get access to a single car's wiring diagram for a reasonable price?

After registering you can get free wiring diagrams here:

www.bbbind.com/tsb-wiring-diagrams-database/

Depending on the vehicle there are more unfused circuits. Starter wiring, cooling fan come to mind.

Instead of pulling fuses you might want to consider measuring voltage drop across the fuses to detect current flow.

Very nice, thanks for the link. I was ready to pay a decent price on an as-needed basis but free is just fine with me!

I did see Paul's video about checking for a voltage drop across the fuses. But I didn't see it until I got home.

Will check the starter & associated wiring.

The fans surprise me. Surely they at least have fusible links or some kind of protection...

500 ma is a huge drain usually they are about 50 ma max with a drain that big the aternator would also have been high on my suspect list. I had 150 ma one n a Freelander that turned out to be the antenna coil on the ignition switch was constantly live and its wiring burned out shorted.

My approach on this would be devide and conquer, try disconnecting the plugs at the rear of the interior fuse box, a clamp dc ammeter or clip on ammeter is your friend with this sort of issue ---

We tried it again on this much warmer day. Whatever it was, it wasn't running through either fuse block. The alternator wire immediately disappeared into a wire loom but fiddling with it never budged the ammeter. The power wire on the starter was easy to get to so we disconnected it and the current draw went from .56 amps to .01. I assume that something in the solenoid is jammed, chafed, or I don't know what. He's getting a new starter today.

I wouldn't have advised pulling the trigger on the starter without doing more checks, as I would have worked on the theory that it was more likely that something upstream was finding a ground through the starter wire.

A test light is the tool of choice on this job, if with a tesst light connected to ground touching the probe end of the test light to the S (solenoid) wire of the starter illuminates the test light there is a fault or short to 12v between the ignition switch and the starter solenoid.

Roger that. Test light in the morning.

With absolutely no disrespect intended, I'm looking at the wiring diagram and it looks like the S terminal runs through a fuse. Whatever this is, it isn't running through either fuse block.

Anyway, it won't take any time to put a test light on there and I do want to learn to do things in a logical sequence. And an unopened starter can be returned.

Well, my bad, I was completely wrong. It was not the solenoid. It wasn't the S wire, there was no voltage on it. But there are 2 wires on the larger nut on the starter. One goes into a loom and heads straight to the battery. The second wire, fairly heavy gauge but nowhere near as heavy as the wire from the battery, disappears into a wire loom that goes I-don't-know-where. The second wire is where the drain is happening. It's time to spend some quality time with the wiring diagrams. But if anyone knows please point me in the right direction...

The purple wire is the S wire and the orange wire spliced to the red is my problem wire. I was suspicious of the splice but I pulled it out of the loom and can't see an issue or change the amount of current draining by wiggling the whole mess.

** Edit - My bad, what I was calling a 'splice' appears to be a fusible link. Gonna solve this one when I get over my bad case of the dumbass...

The other end of the fusible link was the BAT terminal on the alternator. And it was allowing power to go the wrong way, so a bad diode seems likely. The alternator was still under warranty so they gave us a replacement. The parasitic drain is now 10 milliamps instead of 560. I'm sure we checked for this on day one but we somehow missed it...

Good find, glad you've got it fixed
Thanks for posting the solution to the problem

A DC clamp ammeter is a techs best friend on a this kind of job I havea couple and use an inexpensive one a Uni-T UT203 which serves as both my clamp meter and as my general purpose multi meter.

Link to UT203 on Amazon UK

Yes, I didn't realize it until we started on this project but my clamp meter was A/C only. I bought a $25 D/C clamp meter for this project. I think it will be handy in the future.

I admit that we tried to go cheap on information on this one. I don't know how good the $250 manuals are for this car but the $12 downloadable one could be hard to follow. (Couldn't find what I wanted on the free web site.) Finally I just decided that the wiring diagrams were abstract views of the electrical paths and not to be taken literally as far as physical locations. Most of them made it look like the wire to the positive alternator post came off of the fuse block instead of the starter. Realistically, if I had spent more time working on cars and less in the office the past 35 years I might have known this without a wiring diagram...

My favorite part was back at the parts store. A simple diode test showed that current would flow both ways on the alternator. Whatever tester they had in back showed that everything was fine. How do you argue with someone who doesn't even understand a simple diode? The manager made the call and gave us a new alternator.