Mysterious parasitic drain

[corndoggydogg]

Hello all. Hoping someone out there has some insight. My battery drains in about a week if I don't drive it. I have replaced both the battery and the alternator. On top if that, my ammeter shows a ZERO (0) amp draw when off. Is there anything else that could drain the battery? I'm stumped at this point and not sure what to do next. Any input would be greatly appreciated. Thanks!

[mechanicalman]

Originally Posted by corndoggydogg

Hello all. Hoping someone out there has some insight. My battery drains in about a week if I don't drive it. I have replaced both the battery and the alternator. On top if that, my ammeter shows a ZERO (0) amp draw when off. Is there anything else that could drain the battery? I'm stumped at this point and not sure what to do next. Any input would be greatly appreciated. Thanks!

Install a test light between either battery cable and the battery. Remove every single fuse one at a time and see if the draw goes away.

Those ammeters are not sensitive enough to show a small draw.

We need a timeline, what happened first? Was the draw there before the battery was replaced? Was the draw there before the alternator replaced?

SO MANY battery drains are caused by dirty cigarette lighters.

[MARKDTN]

Originally Posted by mechanicalman

Install a test light between either battery cable and the battery. Remove every single fuse one at a time and see if the draw goes away.

Those ammeters are not sensitive enough to show a small draw.

We need a timeline, what happened first? Was the draw there before the battery was replaced? Was the draw there before the alternator replaced?

SO MANY battery drains are caused by dirty cigarette lighters.

Agree. Simple test to get you pointed in the right direction.

[corndoggydogg]

Thanks for the reply, mechanicalman. Here's the timeline:
1) bought the truck in August. Seller told me there was a drain on the battery that he couldn't find.
2) Took truck home, and had the battery tested (it looked brand new). Auto part store told me it was a "bad battery".
3) Purchased new battery.
4) Tested system with ammeter. Showed zero draw.
5) Replaced alternator, just to be safe.
6) Removed cigarette lighter.
7) let truck sit for a week.
8) Dead in the water...

Next step, buy a test light? Any other thoughts? Thanks!

[mechanicalman]

Originally Posted by corndoggydogg

Thanks for the reply, mechanicalman. Here's the timeline:
1) bought the truck in August. Seller told me there was a drain on the battery that he couldn't find.
2) Took truck home, and had the battery tested (it looked brand new). Auto part store told me it was a "bad battery".
3) Purchased new battery.
4) Tested system with ammeter. Showed zero draw.
5) Replaced alternator, just to be safe.
6) Removed cigarette lighter.
7) let truck sit for a week.
8) Dead in the water...

Next step, buy a test light? Any other thoughts? Thanks!

OK I'm not sure if you checked the ammeter in the dash or if you checked it with an external ammeter. A digital ammeter is needed, you don't want more than like 7 milliamps maximum and on that old vehicle should be lots less like maybe 2 milliamps. Cars nowadays have lots of memory to keep alive so they have more static draw.

Did you merely remove the lighter plug or did you un-plug the wire to the lighter? It makes no difference if you only removed the plug.

Test for draw again after the new alternator. If still a draw, un-plug the alternator and try again. Yes, a bad yet still charging alternator can cause a draw.

[71 super]

Try unplugging horn relay under the dash. I have had several that had a horn issue and ended up being the drain

[OldBalls]

Originally Posted by 71 super

Try unplugging horn relay under the dash. I have had several that had a horn issue and ended up being the drain

I know this feed is super old found it really helpful. I randomly had a parasitic draw that pulling fuses didn't resolve. I'm not an electrical wiz so I started to freak out a little. After reading this I pulled the horn relay and BOOM, draw is gone. I guess I should've known I could hear something clicking under the dash.

Only had the Blazer for a month and looking at the POs crappy wiring skills I thought I had a complete rewire on my hands. Luckily I can hold off on that until I'm ready.

Anyway, wanted to say thanks for the helpful tip.

[Lee H]

Newer head unit? Blue tooth on will drain the battery.

[Ol Blue K20]

External regulator that's bad could be the culprit too

[mechanicalman]

Originally Posted by Ol Blue K20

External regulator that's bad could be the culprit too

Doh! Forgot about that you are right. Replaced on in an old Mustang for that. PROBABLY the culprit when the internal regulated alternators have a draw.

[corndoggydogg]

Thanks for all of the input, guys. Here's a bit more info on my predicament:

1) Ammeter:
Before the battery drained down, I used a digital ammeter to test the draw between the battery cable and the battery. Zero (0.00) amp reading. I flipped on the dome light, and the meter lit up. So I assume I was doing it correctly.

2) Alternator:
I upgraded my alternator to an internal model, as per the following: http://67-72chevytrucks.com/vboard/s...d.php?t=119379.

3) Stereo: NONE...

4) Cigarette lighted: lighter only pulled, no wires disconnected.

I assumed that the ammeter would pick up ANYdraw (even the lighter or the horn). Not the case?

Thanks all!

[mechanicalman]

Originally Posted by corndoggydogg

Thanks for all of the input, guys. Here's a bit more info on my predicament:

1) Ammeter:
Before the battery drained down, I used a digital ammeter to test the draw between the battery cable and the battery. Zero (0.00) amp reading. I flipped on the dome light, and the meter lit up. So I assume I was doing it correctly.

2) Alternator:
I upgraded my alternator to an internal model, as per the following: http://67-72chevytrucks.com/vboard/s...d.php?t=119379.

3) Stereo: NONE...

4) Cigarette lighted: lighter only pulled, no wires disconnected.

I assumed that the ammeter would pick up ANYdraw (even the lighter or the horn). Not the case?

Thanks all!

A properly functioning ammeter will pick up any draw, even the lighter and horn.

According to your information, you have no parasitic draw on the electrical system that could make your battery go dead.

Perhaps you have an intermittent draw, or a faulty ammeter.

But, for grins and giggles, try a test light. You might have an accessory that needs voltage input to make it's draw, and the ammeter may not provide it with the continuity that a test light will.

It it lights, then go back through the process of elimination.

[franken]

Disconnect the battery, put a slow charger on the battery for several days (or a higher amp charge for a day). I think people (me included) don't charge batteries long enough. The charging system can maintain a charge if you drive enough, but we don't drive them enough.
The starter draws hundreds of Amps. A slow charge puts tenths of Amps in the battery and a fast charge, or the alternator tens of Amps. Its a slow charging process regardless.
Start the truck, measure the battery voltage, shut the truck off and measure the battery voltage after an hour. Post values.
Disconnect the battery, wait a week and see if it starts after reconnecting.
Test light is a good idea too

[corndoggydogg]

Bought a test light, and it picked up a draw. Looks like a prior owner took it upon himself to do some creative rewiring. The short appears to be on the main red wire that connects to the firewall harness. I pulled all of the fuses, one at a time, and couldn't isolate it. Guess I need to do some more snooping around under the dash. Should this red wire run directly back to the positive battery terminal? That is where it was hooked up. Also, I found the black wire from the firewall harness CUT near the negative battery terminal and tucked away. I assume that is not supposed to be cut? Any idea where that should be connected? Fun times!

[jacmac926]

You could have corrosion inside the connector at the firewall I know I have that issue with my truck that is why I am planning on a painless harness project over the winter
And yes that wire should run over to the battery believe that is how I have seen them it is the main power feed to the fuse box

[davischevy]

Originally Posted by corndoggydogg

Bought a test light, and it picked up a draw. Looks like a prior owner took it upon himself to do some creative rewiring. The short appears to be on the main red wire that connects to the firewall harness. I pulled all of the fuses, one at a time, and couldn't isolate it. Guess I need to do some more snooping around under the dash. Should this red wire run directly back to the positive battery terminal? That is where it was hooked up. Also, I found the black wire from the firewall harness CUT near the negative battery terminal and tucked away. I assume that is not supposed to be cut? Any idea where that should be connected? Fun times!

A 10 guage ground wire should run from the negative battery cable to the passenger fender. Do you have grounds from the cab to the frame and cab to engine?

[mechanicalman]

Originally Posted by corndoggydogg

Bought a test light, and it picked up a draw. Looks like a prior owner took it upon himself to do some creative rewiring. The short appears to be on the main red wire that connects to the firewall harness. I pulled all of the fuses, one at a time, and couldn't isolate it. Guess I need to do some more snooping around under the dash. Should this red wire run directly back to the positive battery terminal? That is where it was hooked up. Also, I found the black wire from the firewall harness CUT near the negative battery terminal and tucked away. I assume that is not supposed to be cut? Any idea where that should be connected? Fun times!

OK, with your test light in position between the battery and the pos cable and lit up from the draw, take the black wire that has been cut and gently, briskly brush it across the neg terminal of the battery and see if the test light goes out for a second. If it DOES go out, then that's a ground that needs hooked up.

Watch out for Mr. Sparky!

Hillbilly logic

[twich3136]

are you running a points distributor? improper wiring could keep the coil powered on all the time when It should power down when the key is turned off.

[jamyers]

I had a slow drain, turned out to be the headlight relays that the PO installed. They were hanging upside down by the wires, and had filled full of water and rusted. They still worked (surprisingly) but were draining the battery slowly through the corrosion.

[jamyers]

I had a slow drain, turned out to be the headlight relays that the PO installed. They were hanging upside down by the wires, and had filled full of water and rusted. They still worked (surprisingly) but were draining the battery slowly through the corrosion.

[corndoggydogg]

After testing just about every circuit, I finally found it. Looks like the alternator is the source of the draw. It's a brand new internally regulated alternator. I had a draw with the prior (stock) externally regulated alternator. Before I start tearing wires out, I thought I'd throw this out there and see if anyone has any suggestions where I should start. Any recommendations? By the way, thanks for the test light suggestion. Definitely a good call and worked better than the ammeter. Thanks all!

[mechanicalman]

Originally Posted by corndoggydogg

After testing just about every circuit, I finally found it. Looks like the alternator is the source of the draw. It's a brand new internally regulated alternator. I had a draw with the prior (stock) externally regulated alternator. Before I start tearing wires out, I thought I'd throw this out there and see if anyone has any suggestions where I should start. Any recommendations? By the way, thanks for the test light suggestion. Definitely a good call and worked better than the ammeter. Thanks all!

It can happen, but the odds of having 2 alternators (or voltage regulators) in a row with a draw are remote. Odds are that circuitry malfunction related to the alternator/regulator (external to them) are stronger.

[corndoggydogg]

I am pulling my hair out. Still unable to fix the problem. Before I begin ripping out wire and installing new, I wanted to make sure I'm on the right track. I "think" the fault is somewhere under the hood. I disconnected the wiring harness on the firewall, and the fault still exists. Is this assumption accurate? I have been focusing all of my energy under the hood. Or is there a way the fault could be on the other side of the firewall? Thanks!

[davischevy]

You haven't mentioned checking the grounds, but assuming you have, hook up the test light, and start unplugging relays, connectors, etc. to try to isolate the problem farther.

I can't stress enough how much trouble a poor ground can cause.

We were detailing a truck a while back, and even though we hadn't had a problem, the wiring looked suspect, and I bought a good used harness off a board member. It took a couple hours to change, and I feel better.

[Andy4639]

I didn't read this whole post so this may are may not apply. But...
Several years ago I swapped over the alternator to the internal regulator. After doing this I noticed my battery would die after sitting for a few days. It ran fine and it would charge up, I checked everything possible and never could fine anything wrong.

By accident one afternoon I discovered the alternator was warm not hot but I hadn't drove the truck since the day before so it wasn't suppose to be warm at all. I got to looking and on the backside of the alternator where the plug in is I got to checking and some how had the wires crossed. I swapped the plug in around and all was good.

Just something to check.