Mysterious parasitic drain

[zosoppp]

Looks like someone spliced a diode into the brown wire. Perhaps it was a misguided attempt to make the generator light go out...

When you tested for continuity on the brown wire, did you try testing both ways (swap test leads from the VOM)?

[zosoppp]

Also while there is a circuit from the battery to ground to alternator body to red lead back to battery positive, inside the alternator, the connection from ground to the big red lead (screw terminal under the boot, not plug connector) goes through the rectifier, which if working correctly should not pass battery voltage through the alternator. If the diodes in the rectifier are bad then it could be the cause of your drain.

Try temporarily disconnecting the big red lead from the alternator (only after disconnecting the battery ground terminal first) then protect the loose red connector (wrap with electrical tape and keep it away from metal, then reconnect the battery and check for leak again. If the "leak" continues then it's not the alternator.

I don't suggest running the engine like this, just to make sure the alternator rectifier isn't bad.

[swamp rat]

You should run this by VetteVet in the electrical section, but i suspect that your truck was converted from idiot lights to guages or Vise Versa, One of them has a resistor wire and the other does not if i'm not mistaken, pretty sure its that brown wire but don't mark my word on it, i'd have to do some research, also schematics are posted over there as well.

http://67-72chevytrucks.com/vboard/f...splay.php?f=64

[VetteVet]

I just saw this thread reposted and I sort of remembered it. I thought he had resolved the problem but I see it is still hanging on. He's getting great advice so I can't add much except for the brown wire that feeds the alternator. It should have power with the keey on and no volts with the key off. It shouldn't need a diode or a resistor unless the internal regulated alternator is the CS style.

What you have to do with a key off drain is to isolate it one step at a time and knowing the circuits is very helpful as well. If it is a hard find then I usually recommend disconnecting the firewall block to isolate the engine compartment from the cab. All the truck power goes through the firewall block to the cab and then back to the front of the truck. The tail light connector and the dome light have different harnesses but they are still fed by the single red wire that goes through the firewall block.

Now this doesn't apply if a person has run power wires to the cab for stereos or other items not normally on the truck.

If he disconnects the firewall block and the drain goes away then it's in the cab. If it stays then it's in the engine bay and we can concentrate on the loads in the engine bay.
Alternator, regulator, horn relay, etc.

The thread posts on the alternator are all accurate and even a new alternator can be bad. That would be one of the things that would show up in the engine compartment as a drain when the firewall plug is disconnected.

Once the drain is isolated then we can start figuring which item is the culprit.

[michael bustamante]

internal reg. alternator right? when you redid the wiring did you hook up one of the wires from the alternator plug into the back of the alt where the 12v+ goes? ive read that this causes a draw and the wire should be hooked up to the 12v+ (red wire) from the old external regulator you bypassed

[Longhorn 70]

Has the ignition switch or the harness been replaced? Even the pigtail going to the ignition switch. I ask because I had a wire that wasn't connected to the switch. It was a tickler wire that got the alternator going at start up so it didn't have to wait for the engine to reach a certain RPM.

This wire is a small 24a.w.g brown/white wire. IF it is connected to hot, it would let the alternator work, charge and be happy but would drain at a slow rate when the engine isn't running. If the alternator is unplugged, it would not draw current.

Just a wild guess. BTW Vette Vet guided me on my fix.

[corndoggydogg]

Originally Posted by zosoppp

Looks like someone spliced a diode into the brown wire. Perhaps it was a misguided attempt to make the generator light go out...

When you tested for continuity on the brown wire, did you try testing both ways (swap test leads from the VOM)?

Yes...tested both ways.

[corndoggydogg]

Originally Posted by VetteVet

I just saw this thread reposted and I sort of remembered it. I thought he had resolved the problem but I see it is still hanging on. He's getting great advice so I can't add much except for the brown wire that feeds the alternator. It should have power with the keey on and no volts with the key off. It shouldn't need a diode or a resistor unless the internal regulated alternator is the CS style.

What you have to do with a key off drain is to isolate it one step at a time and knowing the circuits is very helpful as well. If it is a hard find then I usually recommend disconnecting the firewall block to isolate the engine compartment from the cab. All the truck power goes through the firewall block to the cab and then back to the front of the truck. The tail light connector and the dome light have different harnesses but they are still fed by the single red wire that goes through the firewall block.

Now this doesn't apply if a person has run power wires to the cab for stereos or other items not normally on the truck.

If he disconnects the firewall block and the drain goes away then it's in the cab. If it stays then it's in the engine bay and we can concentrate on the loads in the engine bay.
Alternator, regulator, horn relay, etc.

The thread posts on the alternator are all accurate and even a new alternator can be bad. That would be one of the things that would show up in the engine compartment as a drain when the firewall plug is disconnected.

Once the drain is isolated then we can start figuring which item is the culprit.

Thanks for the info. I was worried I screwed something up by removing that diode. Looks like I have a few things to test later tonight. Here are a few quick points. It has been isolated to the engine bay. The issue DOES persist after unplugging the firewall block. This is a new alternator, originally purchased with the assumption that the original alternator was the drain (and it was an excuse to upgrade to internally regulated). I guess it could be the new alternator, and I will test that tonight as zosopp suggests. I guess I hope it is the alternator...its still under warranty and would make my headaches go away! Will keep you posted. Thanks to everyone for the advice.

[corndoggydogg]

Originally Posted by swamp rat

You should run this by VetteVet in the electrical section, but i suspect that your truck was converted from idiot lights to guages or Vise Versa, One of them has a resistor wire and the other does not if i'm not mistaken, pretty sure its that brown wire but don't mark my word on it, i'd have to do some research, also schematics are posted over there as well.

http://67-72chevytrucks.com/vboard/f...splay.php?f=64

Thanks Swamp Rat. I currently have gauges. No idea if that was original...

[corndoggydogg]

Originally Posted by michael bustamante

internal reg. alternator right? when you redid the wiring did you hook up one of the wires from the alternator plug into the back of the alt where the 12v+ goes? ive read that this causes a draw and the wire should be hooked up to the 12v+ (red wire) from the old external regulator you bypassed

Yes, internal (Ultiima 01-0260). Here's how its wired:

Brown wire from firewall connected to original blue (from old ext. regulated alt.), which runs to the #1 blade on the alternator. Red wire to battery is connected to the plug in back of the alt., jumped to #2 blade. I followed the instructions on this post: http://67-72chevytrucks.com/vboard/s...d.php?t=111296.

Not sure I mentioned this yet, but the draw is reading as .003 on my multi meter.

[Longhorn 70]

3 milliamps is killing the battery in a week? WOW....I recall the stereo memory supply in mine is 3 ma. Are you sure there isn't something else going on? That just doesn't seem like enough to drain that fast.

Just a question, I see that your meter is on the 10A scale. That is the best range to start with. Have you tried the 200mA scale? If so does it show .003 as well? I am just wondering about the accuracy of low readings on the 10A range.

[corndoggydogg]

That is the big "head scratcher" on this. I have never had a big draw show up on the meter. I'll try the 200mA scale tonight. Basically, I have no electronics hooked up to the truck at this point. However, my test light still illuminates when connected between the + battery terminal and positive cable. It only disengages when I pull the harness out of the alternator. But last I tested, the battery drains in a matter of days. Exact same scenario as when I bought the truck, but I have since replaced both the battery and alternator. I am now in the process of tracing out every wire (and removing all of the crap that has been installed over the past 40 years). Could this be a bad ground somewhere? Or maybe a hot wire mis-connected?

[Fitz]

Originally Posted by corndoggydogg

After tracing all visible wires, double-checking grounds, and replacing the wiring harness connector, still no "smoking guns" found. So I moved on to test each individual wire's continuity. The brown wire leading from the firewall to the alternator had NO CONTINUITY. I stripped off the black warness tape to inspect the wire. I'm not sure what it was, but there was something soldered inline, and the continuity ended there. (SEE PHOTOS). I didn't see anything on the wiring drawings, so I cut it out and spliced in a new wire, restoring continuity. Could this be the source of my on-going headaches? Maybe the alternator wasn't charging the battery properly?

Promlem is, my test light still illuminates, and only turns off when I disconnect the alternator harness.

Stupid question(?): Here's how my alternator is wired and it appears to align with the wiring plan (battery negative->ground, ground->alternator, alternator->battery positive). Call me a novice, but doesn't this create a complete circuit that should not result in the test light turning off?

Any info would help and be much appreciated... Thanks all.

That 'thing' you found is a diode. It will allow current to flow in one direction only. Because the test light turns off when the alternator is disconnected you have found your wiring problem. The harness wiring is not compatible with the alternator you have. I suspect that the alternator was not charging due to the diode in that wire. To be certain everything is as it should be, you will need to trace out the entire charging circuit by comparing it to the wiring diagram for your alternator.

[mechanicalman]

Originally Posted by corndoggydogg

That is the big "head scratcher" on this. I have never had a big draw show up on the meter. I'll try the 200mA scale tonight. Basically, I have no electronics hooked up to the truck at this point. However, my test light still illuminates when connected between the + battery terminal and positive cable. It only disengages when I pull the harness out of the alternator. But last I tested, the battery drains in a matter of days. Exact same scenario as when I bought the truck, but I have since replaced both the battery and alternator. I am now in the process of tracing out every wire (and removing all of the crap that has been installed over the past 40 years). Could this be a bad ground somewhere? Or maybe a hot wire mis-connected?

Just for grins and giggles, can you access another known good alternator and try that to see if it eliminates the draw?

If that works to stop the draw, then see if THAT alternator charges if not you might need to do something with that diode and/or related wiring.

[Longhorn 70]

OOOOHHHH>>>>>

In the 80s there were batteries that did this....Exide made a "Red Camel" battery that would sit...then start internally discharging

They got so hot they'd bow the sides. You could jump start them and they'd work again. Then fail again.

I'm not saying that's what's up here....but don't discount a battery because it's new.

[michael bustamante]

when i did my alt. i jumped that wire to the back of the alt too. my battery would die in a week of non use. at least to where the starter wouldnt turn. i rerouted the wire on the alt plug to the 12+ coming from the old external regulator and i never had a problem since

[junior43]

I fought a Corvette with a draw one time. With the test light, I pulled all the fuses, disconnected stuff. Finally ended up being a draw from the starter. Replaced it... problem solved

[kxmotox247]

Looks like a diode has been installed.

Here's verbiage from a Painless Wiring kit regarding installation of these:

NOTE: Under some circumstances, the connection to the Alternator will not allow the
Engine to shut off If this occurs, a diode will have to be installed inline on wire
# 914. This will prevent alternator feedback into the ignition system & allow the
Engine to shut down, The RADIO SHACK part number for this Diode is 276-1661
It is to be installed with the striped end towards the alternator.


Sorry... made a reply without seeing the 2nd page

[corndoggydogg]

Originally Posted by junior43

I fought a Corvette with a draw one time. With the test light, I pulled all the fuses, disconnected stuff. Finally ended up being a draw from the starter. Replaced it... problem solved

Interesting. Did you replace the starter motor, solenoid, or both? Thanks!

[junior43]

I just replaced the whole starter with a reman. So I couldn't tell you which was the real issue. It was a mid 70's Corvette.

[Chucks72Longbed]

That little device is a diode. It only allows power to flow in one direction.

[Chucks72Longbed]

The thing in the pic is a diode. It only let's power flow in on direction. If you put a meter on it will read no continuity one way and if you switch your meter leads it will read continuity. By the way I live in Sedro Woolley. About 70 miles north of you up I-5

[VetteVet]

You should not need a diode in the brown wire from the cab. The factory put a resistance in the wire of about ten ohms which is enough to keep the diodes in the alternator from feeding voltage back to the ignition switch and keeping the engine running when the key was shut off.

The idiot light dashes have a charging light which gives the alternator the ten ohms resistance it needs and also protects the diode trio in the alternator from shorting to ground. The resistance wire from the key switch is used as a backup to the light bulb in case it blows and it also provides the resistance in the wiring to the alternator for the gauge dashes which do not have the light.

If one were to run a 12volt hot wire to the alternator to the no. 1 terminal without this resistance, it might blow the diodes and allow the battery power to drain to ground over time. If someone has wired your truck like that it may explain why you've still got the drain after changing the alternator. It's simple to tell if the alternator is shorted if you have a ohm meter. Just run a continuity test on the no. 1 terminal of the alternator to the alternator case then reverse the leads. If you get zero ohms both ways then the diodes are shorted to ground. Do the same thing on the large terminal on the back of the alternator. I suspect that the no.1 terminal is shorted since you stated that the drain went away when you unplugged the alternator. The no. 2 terminal should be checked also since it is hot all the time. It would drain without the key on.

Refer to this link and you should get all you need to know about the wiring to convert to the internal regulated alternator.

..........http://67-72chevytrucks.com/vboard/s...d.php?t=417872

[Chucks72Longbed]

Don't know if you saw this or not from VettesVet but it's great info on how the system works: thanks to VettesVet!! Here is the message that has just been posted: *************** You should not need a diode in the brown wire from the cab. The factory put a resistance in the wire of about ten ohms which is enough to keep the diodes in the alternator from feeding voltage back to the ignition switch and keeping the engine running when the key was shut off.

The idiot light dashes have a charging light which gives the alternator the ten ohms resistance it needs and also protects the diode trio in the alternator from shorting to ground. The resistance wire from the key switch is used as a backup to the light bulb in case it blows and it also provides the resistance in the wiring to the alternator for the gauge dashes which do not have the light.

If one were to run a 12volt hot wire to the alternator to the no. 1 terminal without this resistance, it might blow the diodes and allow the battery power to drain to ground over time. If someone has wired your truck like that it may explain why you've still got the drain after changing the alternator. It's simple to tell if the alternator is shorted if you have a ohm meter. Just run a continuity test on the no. 1 terminal of the alternator to the alternator case then reverse the leads. If you get zero ohms both ways then the diodes are shorted to ground. Do the same thing on the large terminal on the back of the alternator. I suspect that the no.1 terminal is shorted since you stated that the drain went away when you unplugged the alternator. The no. 2 terminal should be checked also since it is hot all the time. It would drain without the key on.

Refer to this link and you should get all you need to know about the wiring to convert to the internal regulated alternator.

..........<a href="http://67-72chevytrucks.com/vboard/showthread.php?t=417872" target="_blank">http://67-72chevytrucks.com/vboard/s...d.php?t=417872</a> *************** There may be other replies also, but you will not receive any more notifications until you visit the forum again. All the best, The 1947 - Present Chevrolet & GMC Truck Message Board Network

[zellway]

In reading over all this looks like you all have hit the points I was thinking. I don't know if someone hit this but I had a truck the didnt have a horn installed but the ground in the steering column that would lock in the relay and would run the battery dead in a day or two. Sorry if this was a point that has been hit.