The Stovebolt Site Forums The Shop Area The Electrical Bay Voltage drain needs investigation

Driving my 63 one day and my horn starts to blow. Disconnected horn and it stopped.
Usually that’s caused by a short in the column near the upper bearing.
Next day my battery is dead.
Charged battery again but when I checked, I found a 10V voltage drop at the negative battery terminal. The column is completely out of the truck but the 10V drain is still there.
What items should I check first?
Alternator?
Horn relay? (It’s only 6 months old)
Suggestions?
Key ignition switch?

All the lights work properly. No HEI in this truck.
Thanks in advance for your ideas.

Sorry but I and maybe others don’t understand what you mean by “a 10v voltage drop”. Can you explain your problem a little better.

How did you disconnect the horn?

If you disconnected it at the horn, the horn relay is still energized and drawing current. Is the relay warm?

Disconnect the brown wire (one that goes up the column to the button) at the horn relay.

The entire steering column is out of the truck, so the brown wire from the steering wheel is no longer connected to the harness. I reconnected the horn and the horn no longer blows, so I doubt the horn relay is stuck.

When I disconnect the negative cable on the battery, any shorted circuits in the truck can be detected and measured by connecting a digital multimeter between the negative cable and battery ground. I am reading 10V. I did not measure amps (but should have though). A 12V bulb will show (or should show) a 12V voltage drop. A shorted circuit in something else may not show a 12V drop because of the inherent resistance and amp flow. V=IR
It’s not drawing enough current to blow a fuse because if the fuse blows it interrupts the circuit.

If you put the DVM in series with the ground circuit and read 10 volts I would think your battery is weak for whatever reason. A DVM draws very little current in voltage mode, at best a milliampere or so. On the other hand, with all circuits off, you should read zero voltage as that’s an open circuit. On your horn relay, did you remove the horn wire or the voltage side of the relay. If you removed just the horn wire, the relay could still be closed and drawing current if the ground side of the relay is grounded.

Lugnutz,

Using the method you described, you should have had your voltmeter on an 'Amp' setting, and you would have read a current draw off the battery. Current is measured in series; volts in parallel.

I just went out and checked on my truck: on a battery charged to 12.8v, doing what you described yielded a volt reading of 10.2v, slowly climbing to 12.8v before I lost interest. Testing volts in that manner is basically reading the battery voltage through the wiring harness, and doesn't provide any useful information. You haven't hit upon your problem.

Check for a current draw, starting with the battery. Then check current draw on your relay, since you already suspect that. If the draw of the relay isn't nearly your total draw on the battery, then the problem is elsewhere. Current flow is a first-order effect, voltage drop is a secondary effect. (As an example, the stereo in my truck draws about 300mA even when off...running the clock, holding memory presets, etc.)

Think of electricity as water in a pipe...voltage is pressure (psi), current is flow (gpm).

-Kevin

Back to the horn relay.
I doubt the relay is the problem. I’ve hooked the horn back up. No more horn. If relay was stuck the horn should sound.

Jay,
When it's dark outside, look and see if the alternator light on the dash has a dim glow to it. Sometimes when a diode goes bad it will run the battery down. Or you could just disconnect the alternator all together and see if the battery goes down.

If you no longer think it's the horn relay, measure the current draw at the battery as described above. Then start checking each wire attached to the battery circuit of the fusebox.

-Kevin

Connect between the battery and battery cable as stated. Watch the reading as you pull each fuse. When you see the current drop, that circuit is your problem. Also disconnect the alternator feed. If it goes away then, your alternator is the problem.

These are all good suggestions from seasoned diagnosticians.
I thought for sure the problem was in my steering column. Whether that was the case or not, at least it got me motivated to pull out my entire steering column and rebuild it. Now my truck will be safer as a result.
I suspect I will eventually find something wrong with the horn relay. That’s the only thing that really makes any sense. I did not have any problems with a dead battery until the horn problem reared its ugly head. I’ve somehow convinced myself the horn relay is not the problem, but I will check that theory again before tearing anything else apart.

If any of you are interested, you can see my DIY for rebuilding a 1963-1966 steering column in the 1960-1966 forum section.

Good idea! Pulling fuses is probably the easiest way to isolate the current draw.

-Kevin

Got home 11PM And went straight out to the shop. I knew I couldn’t sleep well until I had the answer.
You are correct, my battery is weak and only shows 10V across the posts.
My digital multimeter shows I have a 1 mA current draw from something, but I haven’t figured that out yet.
The horn is reconnected but does not sound when I hook the battery cable up again. The horn relay is only six months old. I disconnected the horn and just tested the horn relay by supplying a ground to the correct prong. There is an audible click and the meter shows voltage to the wire that goes to the horn immediately jumps to 10V (which is what my weak battery is showing right now).

If you are sure you have set the multimeter probes into the correct jacks and you are actually only reading one (1) Milliamp, that is static electric in the air from you or the meter or the wind or outer space. Start by suspecting a bad battery or a bad charging system. Check battery voltage with cables off and see if it reads 12.6V. You probably just have a dead battery.
I really can't believe you can measure 1 ma. Also a "1" is displayed on some meters to mean "open circuit".
A reading of 1 ma is ZERO drain.
ESD can be measured in amps or volts using a multimeter.

Hope you do not have some fancy modern thing in your truck, that you forgot, and has a light or hold up in it as Shakey said. Anything that will display time or date has a hold up. Theft system has a hold up. Music/USB/GPS/radar detector ports may have drain.

No fancy add on devices.
Here’s two pics to check my diagnostic work.
Weak battery is why I have only 10V.

Your first pic is confusing. You have the positive (red) DVM lead connected to the negative battery lead. I assume the black lead is on the negative battery post. This setup would degrade the battery voltage by any load your system has including your problem. If all your systems are off, I would think you should read zero volts as the battery should be disconnected from your electrical system. Anything like the radio memory or clock should not drop that much voltage.
I had this problem which was caused by a leaking diode pack in the alternator. Do you know how to check the alternator?

The 1.03 ma looks correct if you have the meter in series. No drain.
The 10.24V looks like you are not measure properly. I don't know where the meter leads are attached. Should be touching the battery posts. The voltage measurement is taken in parallel not in series like the amp reading.

This whole process has made me come to realize that my battery is no good. I just finished re-charging the battery and it only reads 10.5 V across the posts.
The first photo shows Less than 12 V because I have a bad battery. The multimeter is measuring in series with the negative battery terminal and the disconnected negative battery cable.

So it seems that everyone is of the opinion that 1.03 mA is no big deal. I will try to figure out where it’s coming from none the less. As far as why the horn began to blow on its own, I suspect that it was something in the steering column after all. Now that the steering column has been removed from the truck, the horn does not blow.
I’m assuming that 10.5 V would be enough to trigger the relay if there was a problem.

Laugh at me if you want, but here is what I think happened the day my horn started blowing all by itself.
1. Something in my steering column caused a ground connection to the brown wire that goes to the horn relay.
2. I unplugged the wire to the horn but the relay was still activated by the ground.
3. The still activated relay drained my battery.
4. Once the battery was dead, the relay disconnected internally.
5. Since removing the steering column from the truck, the ground to the horn relay has been eliminated.
6. I’ve discovered an incidental 1 mA drain on the battery that has nothing to do with the original horn problem.
7. I need a new battery. My battery must have been on its last leg because even after charging, it’s still not able to deliver 12V.

Sounds plausible. Relays will often engage, and the load draws the voltage down, causing the relay to drop out, and the battery recovers allowing the relay to re-engage,causing the voltage to drop, etc. etc. That's the reason you get the "click-click-click" on a starter relay with a low battery.

Not laughing at all. This is troubleshooting 101, DIY style. It's very easy to misdiagnose and chase your trail. I've done it many times and am trying to get smarter. Thanks for keeping us updated, This is how we all learn together. Many good ideas and suggestions on this post with you doing all the hard work. Hope the new battery and rebuilt/rewired column gives good results.

Tests you need to do in the future with new battery.
1. Test battery at rest. Test across the posts and get 12.6V or close. Battery good.
2. Test battery, motor running. Test across post, and then across post clamps, to get 14V or close. Alternator good.

Good find Lugzy! I was getting ready to post that "I told you so," but I never made a post at all until this one

Good job!

-Kevin

My battery drains 2mA...as the alternator shows a resistance of 5.8k... Im not sure if that is standard...either way,..something else to investigate.

A single garden-variety LED draws 20mA when lit. Unless your meter can read down to μA, 1 or 2 mA is a rounding error, and of no concern. My cigarette-lighter USB charger has a blue LED for backlighting, so there's 20mA even when nothing is plugged into it.

-Kevin