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Old 09-29-2017, 05:32 PM   #1
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Question Battery Drain

Just installed a Vintage Air kit into my '72 GMC 1/2 ton. Getting ready to charge the system and noticed I'm getting a battery drain. So went through the prescribed analysis. Disconnected the voltage regulator and drain goes away. Replaced the voltage regulator, but still have the drain when I hook up the new voltage regulator. I'm betting it's not the regulator but something else, but don't know where to go from here. Ideas?
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Old 09-30-2017, 09:19 AM   #2
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Re: Battery Drain

Disconnect the alternator and check. If that's not it then start pulling fuses one at a time to see if it goes away.
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Old 09-30-2017, 11:57 AM   #3
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Re: Battery Drain

Thanks. Since a large portion of the battery drain goes away when I disconnect the voltage regulator, I was thinking that was the culprit. I put in a new VR, but got same results. No change when disconnecting the alternator. My meter is giving me about 630mA draw with VR connected. Drops to 17mA when VR is disconnected. Does it still make sense to pull fuses?
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Old 09-30-2017, 03:24 PM   #4
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Re: Battery Drain

There are two power wires to the voltage regulator, The red one is connected to the battery and large alternator junction, and the brown one which goes directly from the key switch to the regulator. The red wire should have voltage on it all the time and the brown wire should only have voltage on it when the key switch is on.

Have you checked the drain with both the regulator and the alternator disconnected?
This includes the large red wire on the alternator.

A .017 ma drain is still too much drain.I think .004 milliamps is the maximum.That is read as 17 milliamp and 4 Milliamps. If you had a bad diode in the alternator it could drain from the large red wire through the diode to ground.

The fuses that protect the key on circuits will not have voltage on them with the key off unless there is a wiring problem. You would be seeing something on like a light or a fan.

I would check the wiring on the vintage air system power supply to the switch if you're still pulling 17 milliamps after disconnecting the VR and the alternator and checking the voltage on the brown wire.
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Old 09-30-2017, 04:07 PM   #5
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Question Re: Battery Drain

I only disconnected the red battery wire from the alternator when checking. I have now also pulled out the plug (blue and white) from the alternator. The amp reading with the VR and all alternator wires disconnected is now 1.5mA. I checked voltage on the red and brown wire at the VR plug and I have voltage on both wires with key off, the readings are the same at about 1.1 volts.
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Old 09-30-2017, 08:06 PM   #6
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Re: Battery Drain

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Originally Posted by Goose View Post
I only disconnected the red battery wire from the alternator when checking. I have now also pulled out the plug (blue and white) from the alternator. The amp reading with the VR and all alternator wires disconnected is now 1.5mA. I checked voltage on the red and brown wire at the VR plug and I have voltage on both wires with key off, the readings are the same at about 1.1 volts.


The red wire should read 12 volts (battery volts) as long as the battery is connected. The brown wire should read 12 volts with the key on and zero with the key off. You should do a continuity check on the alternator between the large post and the alternator body for zero ohms and continuity when you reverse the leads.

Here is the wiring diagram and you can see the red VR wire connects with the battery and alternator charge wire. so they all will read battery voltage.

ATTACH]1694773[/ATTACH]
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Old 09-30-2017, 10:26 PM   #7
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Re: Battery Drain

Thanks very much. I'll give this a try tomorrow. I appreciate your patience and wiring diagrams. Your diagrams are considerably clearer than my factory assembly manual.
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Old 10-01-2017, 03:12 PM   #8
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Re: Battery Drain

I am measuring over 12 volts on the red wire; and with the key off I am also measuring over 12 volts on the brown wire. I read about 1500 on the 2000k ohm scale between the battery post and the casing of the alternator. If I'm getting voltage on the brown wire with key off, is it the ignition switch giving me problems?
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Old 10-01-2017, 09:32 PM   #9
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Re: Battery Drain

12 volts on the brown wire means that either the key switch is bleeding through to the accessory terminal or the accessory wire is getting power from the fuse panel key off circuits and is powering the brown wire. They both share the same terminal on the key switch so the accessory side should be getting power with the key on only. The accessory wire powers the turn signals, the wiper motor, the heater fan switch and maybe one other thing. If you put themeter on the brown wire and pull those fuses you may be able to tell which one is baccfeeding the large 12 gauge brown accessory wire.

You need to know that the small 24 gauge brown wire, actually b/w striped resistance wire (10 ohm), is the same wire from the key switch that converts to a 16 gauge brown wire on the engine side of the firewall.

This wire is the alternator exciter wire and it runs to the voltage regulator plug and powers the white wire to the alternator to excite the field in the alternator to start it charging. This is a power circuit to ground and is the main reason you have a drain because it has power with the key off.

Here's the wiring for the accessory wire and the b/w stripe resistance wire from the key switch to the fuse panel (ACC wire ) and the resistance wire to the inside of the cab.

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come to think of it, if you have power on the brown VR wire you must have power on the ACC wire since they are connected at the key switch.

If you pull the key switch plug and you still have power on the brown wires it must be coming from the fuse panel, and if you pull the ACC wire on the back of the fuse panel and you still have power it must be the key switch.

I would double check the wiring for the Vintage air unit power supply.
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Old 10-01-2017, 10:11 PM   #10
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Re: Battery Drain

Ok, thanks. When I was wiring up the VA system it looked like I had accidently pulled a single brown wire off the ignition switch module. I just put it back on the empty peg, so may have inadvertently created my own problem. I'll pull that brown wire of the ignition module and see what happens to the key off power on the brown wire at the VR. Although looking at the ignition switch wiring diagram I see the combined 12 brn 4A and 24 Brn 130 which implies two wires spliced at back of the switch. Mine seemingly was a single brown wire. Also rechecking the wiring on the VA system although it was fairly self explanatory - famous last words. I appreciate your thoughts.
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Old 10-02-2017, 05:35 PM   #11
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Re: Battery Drain

VetteVet - thanks very much for you help and patience. I have the battery drain down considerably from what I had. I have an internal VR alternator rebuilt and setting on the shelf so I think that will be my next project once I get the truck back on it's feet. You folks have provided lots of guidance on that process, so if I just follow instructions it should go smoothly.
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Old 10-02-2017, 10:32 PM   #12
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Re: Battery Drain

Quote:
Originally Posted by Goose View Post
VetteVet - thanks very much for you help and patience. I have the battery drain down considerably from what I had. I have an internal VR alternator rebuilt and setting on the shelf so I think that will be my next project once I get the truck back on it's feet. You folks have provided lots of guidance on that process, so if I just follow instructions it should go smoothly.
We're going out of state this weekend but I'm going to try to get online when I can. The IR alternator is very easy to wire but solve your drain issue first.VV
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