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Discussion Starter #1
I have had a problem with the charging system on my GT after taking out of storage and driving it to a car show. It worked fine all day but the next morning the battery was dead. I found no shorts or anything on. I had the charging system tested at Oreilly's and they said the battery was good (whew! Red Top) - bad Voltage regulator. I tried another one... same thing. I ordered a new VR from them and a couple days later put it on and went back to them, they said VR was still showing bad. I didn't believe them and instead ordered a reman alternator from RockAuto. I put it on today and the amp gauge is showing 30amps at idle. I believe everything to be hooked up correctly after installation. I tried a diff VR and it shows the same thing. Would it be high if the battery were fairly drained?? I don't think the alternator should be putting out 30 amps at idle assuming it is reading correctly. Normally, it sits slightly to the right of 0 until you turn something on. Any thoughts? The rebuilt alternator is bad?
 

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Opel Rallier since 1977
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If the battery has not been re-charged after it ran down, then the ammeter WILL shows a high charge current until the car is driven for 20-30 minutes and the battery gets charged.

Go and buy a volt-ohm meter right now before you do anything else. Not one to put in the car, but one to test with. Start the car and measure the voltage across the battery terminals with the engine idling at 1500-2000 RPM. The measured voltage on the battery terminal should be in the range of 13.6 to 14.4, maybe a bit + or - but in that range.
 

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Discussion Starter #3
17 volts at idle! There must be something wrong with the alternator. Tried a diff regulator. Same thing.
 

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Just Some Dude in Jersey
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I've had a LOT of trouble with my GT's eating batteries over the years. I've gone through dozens of batteries. I'm so paranoid that the only time my car isn't on a charger is when I'm driving it. As soon as I park it in the garage I attach the trickle charger. Do not charge your battery on the "fast" setting, if your charger has one. Not good long term. Use the lowest setting. I put external charging posts on my car to make the charger hook up easier. You might have poorly connecting or corroded wires or terminals. When testing battery voltage at various times, make sure to put the voltmeter probe on the terminal itself, not the wire clamp, you want to make sure you're testing what the battery is getting, not what's in the wire.
 

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I've had a LOT of trouble with my GT's eating batteries over the years. I've gone through dozens of batteries.
Well, clearly there's a parasitic load somewhere that you don't know about.

I'd throw an ammeter across your terminals and see just how many milliamps it's sucking.

And, instead of the annoyance of plugging in non-stop, why not instead just get a little dash-mounted solar charger? Usually it's plenty enough to tackle small drains somewhere. They're cheap.
 

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Check the wiring harness between the regulator and the alternator. I had a similar issue because one of the connections was loose due to a partially melted connector housing. As a result, the alternator went "full on" and burned itself and the regulator up. OGTS sells replacement cables.

Good luck!
 

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Opel Rallier since 1977
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Yes, you have a serious regulation problem OP. It's not at all likely to be in the alternator... it is putting out what is commanded to it by the regulator. The regulator senses what the system voltage is, and then uses that to tell the alternator how hard to charge. The problem could be in the regulator, or it could be in the wiring TO the regulator that the regulator uses to sense the system voltage.

Turn the ignition switch to RUN but do not start the car. Is the generator idiot light glowing? If not, then the problem is probably in the light blue wire with the white tracer that connects from the main harness into the regulator-to-alternator harness. There is a fusible link where it connects to the regulator-to-alternator harness; that is a soft, floppy section of wire. If that is burned out, then the regulator cannot sense the system voltage. The link needs to be replaced by another link or a fuse.

Here is a source of the info and wiring diagram that you might find useful; the charging system diagram is near the end. https://www.opelgtsource.com/system/notes/files/000/000/017/original/17OpelGTElectricalSystemNotes.pdf?1540360105
 

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Can Opeler
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See the above link. Don’t spend any more money on it. The alternator harness is just mis wired somewhere. Check everything on that little plug in back of the alternator and voltage regulator. Use the ohm function on your multimeter and make sure that you have continuity on both sides of each wire and that the idiot light in the amp meter glows.

It’s usually the voltage regulator that causes this problem, but the wiring to the regulator can also cause this.
 
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RunOpel
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I have not had this issue as of yet (knock on wood), but really great advice from all :) I hope you solve the issue Scott and when you do, please let us know what you discovered.
 

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Discussion Starter #10
Thanks for all the advice. Ill check out the harness and the link. The harness was a new one from Gil. Hoping it is not melted. Likely the fusible link. Ill check and let you guys know. I put an old alternator back on and the amps and voltage went back down. It could be that the rebuilt one is mis-wired.
 

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Probably not helpful at all, but funny story. Sometime back I had a problem with the battery going down on the GT when it sat for awhile. Could not figure it out for the longest time. Happened to go into the garage one evening after dark and noticed the dome light on. Shut it off, no more problem.
 

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Can Opeler
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Probably not helpful at all, but funny story. Sometime back I had a problem with the battery going down on the GT when it sat for awhile. Could not figure it out for the longest time. Happened to go into the garage one evening after dark and noticed the dome light on. Shut it off, no more problem.
I have really small light motorcycle batteries in both of my GTs. My clock will drain those suckers to 11.5V in a couple weeks. I can hear those dang clock solenoids through my garage wall when it’s really quiet in my house.
Tick tick tick tick THUUUUNK tick tick tick tick. Lol
 
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Just Some Dude in Jersey
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Well, clearly there's a parasitic load somewhere that you don't know about.

I'd throw an ammeter across your terminals and see just how many milliamps it's sucking.

And, instead of the annoyance of plugging in non-stop, why not instead just get a little dash-mounted solar charger? Usually it's plenty enough to tackle small drains somewhere. They're cheap.

All 5 of my GT's over 40 years had issues with batteries draining down. It's a common problem that many of us suffer. There's a number of threads on this site about the lengths that some people have gone to to stop it. The best seems to be to install a battery disconnect, like from a boat, somewhere. I had one under and behind the seat in the car that I put 225K miles on and drove daily to work. Before that, if I didn't drive it for 3 days I'd have a weak battery. The concensus is that it's hysteresis loss at all the various connectors and unused terminals. Of course, disconnecting your battery causes you to lose any presets or programming in your radio.

My present car has an aftermarket fuse box and wiring and all the gauges and stuff are newer, more modern, ones, so the problem coming from the wiring/fuse box/and device connections is diminished. But I have a bunch of electrical devices. I have to have door poppers because the PO removed the door handles. That has to stay partially on in order to receive the signal from the remote. I have decorative plasma plates in the back that may or may not be drawing some current to charge up capacitors, even though they're off 99% of the time. My car is always stored in a garage, so a solar charger on the dash wouldn't help me. I only drive the car on weekends and I have those external battery posts just in front of my left front wheel well, so it's really not a big deal for me to clamp the charger onto them. However, I'm a dumbass and I keep forgetting to disconnect the charger before going for a drive. Luckily there's a "dumbass disconnect" on the charger that unplugs when I roar off into the sunset. I made my own "dumbass defeat device" : I have a big yellow sign that I always carry in the car that I prop up on the dash to block the windshield. It says: "UNPLUG THE CHARGER DUMBASS!"

🤪
 

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The concensus is that it's hysteresis loss at all the various connectors and unused terminals.
Hmm, no, that's not how that works. Not with DC, and not at 12v.

It's either a near-short or it's some device with draw. Someone mentioned the clock, that could do it. Anything that's still on when the car is off.

You wouldn't think that's a problem on a 50 year old vehicle, off should just mean off.

Of course, disconnecting your battery causes you to lose any presets or programming in your radio.
I guess if that's your only reason to not flick a battery disconnect, you could leave that one connected.

I have to have door poppers because the PO removed the door handles. That has to stay partially on in order to receive the signal from the remote.
Still, modern cars have this, and you can leave those for months without killing the battery.

I have decorative plasma plates in the back that may or may not be drawing some current to charge up capacitors, even though they're off 99% of the time.
If the switch to them is off, they're off. If they have a power supply that is always connected and you only turn on the device itself, then yeah, it'll draw power, more if it's poorly designed.

My car is always stored in a garage, so a solar charger on the dash wouldn't help me.
Hmm, if your garage has a window it might be enough. Might need to throw a joule thief circuit on it to boost the voltage. Depends how fast your drain is.

Luckily there's a "dumbass disconnect" on the charger that unplugs when I roar off into the sunset.
Magnets conduct electricity, you could just use a pair of those. One facing north, the other south, and a matching pair on car. That way you don't have to look which way to plug it in, it automatically flips itself the correct way.

Apple laptops used to (maybe still do?) use a connector like that. You barely have to think about it, just get it generally close and it finds its way home. Drive away and it doesn't hurt it any to get yanked out.
 

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Thanks for all the advice. Ill check out the harness and the link. The harness was a new one from Gil. Hoping it is not melted. Likely the fusible link. Ill check and let you guys know. I put an old alternator back on and the amps and voltage went back down. It could be that the rebuilt one is mis-wired.
When you say the voltage went down with the old alternator what voltage did it go down to? Remember, make these voltage measurements only at a fast idle, like 1500-200 RPM and make them across the battery terminals.

Is the generator light working normally?

We need plenty of feedback on the details of what you find and measure if we are going to be able to help. It is hard to see your voltmeter through the internet....!
 

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Discussion Starter #16 (Edited)
Yes, you have a serious regulation problem OP. It's not at all likely to be in the alternator... it is putting out what is commanded to it by the regulator. The regulator senses what the system voltage is, and then uses that to tell the alternator how hard to charge. The problem could be in the regulator, or it could be in the wiring TO the regulator that the regulator uses to sense the system voltage.

Turn the ignition switch to RUN but do not start the car. Is the generator idiot light glowing? If not, then the problem is probably in the light blue wire with the white tracer that connects from the main harness into the regulator-to-alternator harness. There is a fusible link where it connects to the regulator-to-alternator harness; that is a soft, floppy section of wire. If that is burned out, then the regulator cannot sense the system voltage. The link needs to be replaced by another link or a fuse.

Here is a source of the info and wiring diagram that you might find useful; the charging system diagram is near the end. https://www.opelgtsource.com/system/notes/files/000/000/017/original/17OpelGTElectricalSystemNotes.pdf?1540360105
When you say the voltage went down with the old alternator what voltage did it go down to? Remember, make these voltage measurements only at a fast idle, like 1500-200 RPM and make them across the battery terminals.

Is the generator light working normally?

We need plenty of feedback on the details of what you find and measure if we are going to be able to help. It is hard to see your voltmeter through the internet....!
Sorry. Voltage at idle (about 1500 rpms) went to 13.something and amp gauge started acting normal - just above zero and fluctuating when something is turned on in compensation. I have a battery disconnect on the battery and have been disconnecting it at night. At present, I do not see an amp draw. I am going to leave it hooked up tonight to see if it goes down. I have checked the voltage regulator harness and verified continuity across the fusible link to the fuse box. No issues anywhere. I had also tried multiple voltage regulators with that rebuilt alternator - one was brand new and they all did the same thing. High voltage. Now old Alt is normal.

Gordon, I have all my plasma displays disconnected, have turned off the flux capacitor ( I know you have one of those too!) and ejected the warp core! 😀.
 

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OK, if in the high 13's then that is OK.

Low 13's is not.... If that, it might be a poor regulator, but you have changed that. So might be a diode blown in the old alternator.

BTW, never disconnect the battery with the alternator system running.... some of those old electro-mechanical regulators would readily burn up if you did that.

And a good charged battery will show 12.6-12.7 volts disconnected and after 'resting' (not being charged or discharged) for at least 30 minutes. So you might go out in the AM and check that, after disconnecting the battery for 30 minutes. If low, then the battery may need to be charged, or you have a discharge somewhere.

If you have noticed, your voltmeter is a your best troubleshooting tool for these systems.
 

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Thanks, the SciFi Guy, I've joined your club. "However, I'm a dumbass and I keep forgetting to disconnect the charger before going for a drive ". On one of my other cars, the battery tender was connected to the battery in the trunk. I drove off without disconnecting the tender. I thought people were waving at me as i drove down the road and I smiled and waved back. It was only at a traffic light when the car beside me said that there was something dangling behind my car. I now put a sign on the windshield to remind me to disconnect the tender.

Be safe.
 

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Discussion Starter #20
So might be a diode blown in the old alternator.
I wondered. Seems like the Alternator makes all the difference in my situation. I keep coming back to it and think that I just got a crummy rebuild from Rock Auto. The old alternator drained the battery with a short, the new one had some other crazy problem. At least thats what I am thinking.


BTW, never disconnect the battery with the alternator system running.... some of those old electro-mechanical regulators would readily burn up if you did that.
Good to know. Thanks!
So this morning, I got right up and came out to check the car before I read your post. It cranked good and started right up. I had installed a new Weber from Gil yesterday evening and was anxious to give it a spin. I should have checked the battery voltage first! Duh. Anyway I drove it around and the Carb is fantastic.
So after the drive the battery sitting with the motor off is 12.59V. Started and revving to 2500rpms it only just slightly over 13V. Not sure if I should worry or not. At idle its just at around the 12.59 mark.

If you have noticed, your voltmeter is a your best troubleshooting tool for these systems.
Yes, thanks. I figured. I have not had a lot of issue with the charging system with my past GTs and do not know what the measurements are supposed to be under what circumstances or how the alternator/VR interacts.
I have another rebuilt Alt from Oreillys coming tomorrow to replace the parts car atrocity that I have in there now. Hoping it acts normally.
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