Battery light on, car off

[RedDMC]

Alright, this is a new one for me. My battery drained down after a few weeks of no use. Well, after charging it on a battery charger I reconnected the battery. I walked away and came back to notice the battery light was fully on, no keys in the ignition. I started the car, the light went off but the voltage gauge registered zero. Car was running fine. Revving the engine brought the volts up to 10-12 but they dropped when the rpms dropped. The lights also got very bright with each rev of the engine and that battery light would light up. My first instinct is voltage regulator in the alternator. Otherwise, I'm stumped. I turned the car off and disconnected the battery. Ive done no more investigation. Thoughts?

[hmcelraft]

"Inside" would depend on the alternator you are using I guess. You did nothing else but charge the battery while it was disconnected? Strange - but, ............ You might find a shop or parts store that can check the alternator for you.

[DMCMW Dave]

Disconnect the small brown wire(s) from the alternator. If the light goes off, the alternator regulator is bad.

[David T]

Disconnect the small brown wire(s) from the alternator. If the light goes off, the alternator regulator is bad.

If the light was on with no key in the ignition (and assuming it was in the off/locked position) and further assuming the wiring in the car is intact and original, the main relay is stuck on. No way is that light supposed to be on if the ignition is off. That light (and all of the other loads) will kill the battery. Pull the relay and see if the light goes out. This is not saying the alternator is bad, at least not yet. If the key is on and the motor isn't running the light SHOULD be on indicating the alternator is not charging.

[RedDMC]

Alright, David T, I shall give that a go tonight. That would be really simple, but I have always been under the impression that the main relay hardly ever gives up the ghost (I guess it's 32 years old now though). The only thing that I did not mention was that my alternator is a GM (Delco) unit that I installed some 15 years ago. It just seems very strange that this should happen, while the battery is out, with no other signs. I should also add that my positive terminal seemed a bit on the warm side when I was disconnecting the battery again last night. A friend of mine suggests that perhaps the battery is bad and grounding itself internally. Who knows at this point.

[Bitsyncmaster]

It's probably just the regulator. It must be pumping current back (reversed) into the battery light. If the main relay was stuck on, you would get the oil an other lights on.

[David T]

It's probably just the regulator. It must be pumping current back (reversed) into the battery light. If the main relay was stuck on, you would get the oil an other lights on.

Well, somehow the end of the wire going from the alternator to the light and then to the main relay is connected to something. When that relay is deenergized it is supposed to disconnect that wire. Without a complete circuit how is that light lighting up? I agree other lights should also be lit. That is why I mentioned the wiring may be hacked. Pulling that relay is just a step in the process. If the light remains lit with that relay pulled it will confirm a wiring hack.

[Bitsyncmaster]

Well, somehow the end of the wire going from the alternator to the light and then to the main relay is connected to something. When that relay is deenergized it is supposed to disconnect that wire. Without a complete circuit how is that light lighting up? I agree other lights should also be lit. That is why I mentioned the wiring may be hacked. Pulling that relay is just a step in the process. If the light remains lit with that relay pulled it will confirm a wiring hack.

It drives many things that each have a little resistance. Add all those parallel connections up and I bet you measure zero ohms to ground when the main relay is open.

[Ron]

...
The only thing that I did not mention was that my alternator is a GM (Delco) unit that I installed some 15 years ago. It just seems very strange that this should happen, while the battery is out, with no other signs. I should also add that my positive terminal seemed a bit on the warm side when I was disconnecting the battery again last night. A friend of mine suggests that perhaps the battery is bad and grounding itself internally. Who knows at this point.
Is sounds like a common failure in Delco units, the Diode Trio. This is probably the source of power David T mentioned. You can test it by removing it, connecting one lead of an ohm meter to the single terminal and the other to each of the other three. Then repeat, reversing the leads. One way they should all read like a short (zero), and the other way, infinite (or very high). If it is bad, you have a 50-50 chance that the regulator and/or a main diode(s) are shot too.
Most auto parts can check for this, if you pull it off.

If the battery was shorted internally, it would be dead in a very short while, even if disconnected.

[RedDMC]

I've had the car since 95, so while not totally out of the question, I'd be surprised if there were a hack I didn't already know about. I agree though that there is something providing power bypassing the normal ignition circuit. I'll check it out this weekend and report back. If I'm not mistaken, there is a brown/yellow wire from the alternator to the battery light and the battery light then grounds at the common gauge ground bundle to the main ground post. I'm not too sure because the colored diargram and the original in the shop manual seem to contradict each other. From John Hervey's site:

http://www.specialtauto.com/delorean-parts/images/alternator.jpg

[RedDMC]

Thanks, for the input. Here I thought I was going to be doing a suspension upgrade this weekend.

[Ron]

Note in your link that the even stock alternators (Ducy, the one shown, and Motorola) were wired differently... the Delco uses the main and N/Y wire only.

[RedDMC]

Noted. I wish I weren't in the office today so that I could look at the actual beast.

[NightFlyer]

Note in your link that the even stock alternators (Ducy, the one shown, and Motorola) were wired differently... the Delco uses the main and N/Y wire only.

The Ducey is the BEST alternator for our cars :thumbup:

[David T]

I've had the car since 95, so while not totally out of the question, I'd be surprised if there were a hack I didn't already know about. I agree though that there is something providing power bypassing the normal ignition circuit. I'll check it out this weekend and report back. If I'm not mistaken, there is a brown/yellow wire from the alternator to the battery light and the battery light then grounds at the common gauge ground bundle to the main ground post. I'm not too sure because the colored diargram and the original in the shop manual seem to contradict each other. From John Hervey's site:

http://www.specialtauto.com/delorean-parts/images/alternator.jpg

That wire goes from the alternator to the bulb, on to the relay, through a fuse and then back to the battery. With all of the things wired into the circuit maybe there is some kind of backfeed getting power into that bulb circuit. A blown diode bridge should not cause the light to go on with the ignition off. That circuit is a "sense" line to the alternator basically turning it on when the key is on. NEVER use an LED bulb in this circuit. For it to function properly it requires an incandescent bulb.

[Ron]

That wire goes from the alternator to the bulb, on to the relay, through a fuse and then back to the battery. With all of the things wired into the circuit maybe there is some kind of backfeed getting power into that bulb circuit. A blown diode bridge should not cause the light to go on with the ignition off. That circuit is a "sense" line to the alternator basically turning it on when the key is on. NEVER use an LED bulb in this circuit. For it to function properly it requires an incandescent bulb.OOPS- You have the fuse and the relay in reverse order.

$.04
I agree, a blown diode in the bridge rectifier should not cause the light to go on with the ignition off (yet it would when running...), but a shorted one could on a Delco in a D. The path could be: battery +, shorted + rectifier diode, trio, regulator, lamp, anything else connected to the lamp feed (E.G. gauges...), ground. If disconnecting the Brown/Yellow wire turns the light out, the alternator is #1 suspect, as Dave S said. To confirm, with the switch off, disconnect the Brown/Yellow wire from the alternator and connect a meter between ground and the light terminal on the alternator. If there is power there, it's the alternator -- If not, the power would be on the Brown/Yellow wire, indicating a short in the wiring...

Note the intended Delco 10SI wiring (below)...the switch is usually the only thing connected to the feed side of the lamp (unlike a D) so there is no path "backwards" to ground through other components.
(Some do not have the bleeder resistor shown):
26658

[RedDMC]

Well, Step 1 - Old Battery was bad. This didn't fix the issue, but it's one thing out of the way.

Here's a question, so the fuse 5 is powered by the white wire running from the Auxiliary relay. The white wire goes green on the other side of fuse 5 and that is the power for all of the instrument lights etc. It would seem like if the main relay were stuck closed, thus providing power to the aux relay, which then provides power to the instrument lights, then my a/c panel lights should be on (like the battery light) with the key off since they share a common power source and are always on. I guess the ignition switch keeps them from being on because it completes their circuit? If that is so, I would have to wager that I am down to either a back feed through the alternator being internally grounded somehow, or a splice in my brown/yellow wire to the bulb. (I know, I know, just pull the wire already and see what happens).

I'm just thinking out loud.

[RedDMC]

Ron, I just read your post after my insane raving on. You are right, test light to the light terminal. That ought to answer that hypothesis pretty quickly.

[Ron]

You were all over it already dude! :headbang: {Why isn't this icon called ":rockon:" ? ;-)

[RedDMC]

Ok, so alternator checked out fine. I noticed though that my tach was reading 2k when the car was off. That reminded me of when I had to replace the rpm relay. So I took it out, tested continuity between between posts and I had some between the middle posts. Well, the only thing missing was that my fuel pump was still working. It died shortly thereafter, as if on cue. I jumpered those pins and it worked. So, long story short, rpm relay is bad. I have no idea how it caused my battery light to come on with the car off. I'll order a new relay in the morning and go from there.

[Ron]

DeLorean tachometers don't have a zero function.

I just noticed you said, "...test light to the light terminal." Did you measure voltage from ground to light wire and ground to light terminal?
Unplug the alternator?
Just double checking for clarity on my end....

[RedDMC]

Yes, I remember that the RPM needle is balanced to 2-3 or something, but my point was it reminded me to check the RPM relay. (I have a Hervey relay in there, it's about 7-8 years old FWIW). I removed it and checked continuity, then replaced it and for whatever reason it gave up the ghost completely. I guess I don't know if that will fix my issue, but it needs to be fixed as the relay no longer drives the fuel pump as it is supposed to do. I also ordered a new main relay. Changing both of those should remove them from the list of possible suspects.

To answer your question. I disconnected the brown/yellow wire and tested with a test light clamped to the ground strap on the frame. I tested the terminal to which the brown/yellow attaches, no light. I tested the wire lead, no light.

The news now is that the battery light is no longer coming on when the car is off. My issue now is that the battery light comes on when the engine is revved and gets brighter the higher I rev the engine. My voltmeter is clocking above 13 with the new battery in. I failed to check to see if there was a draw on the battery when I rev the engine.

Yes, this one is a stumper. If it turns out to be neither the RPM relay, nor the Main, I will be at a loss.

[RedDMC]

After reading this thread: http://dmctalk.org/showthread.php?4366-Trouble-with-the-battery-light&highlight=battery+light+bright. I've decided I probably need to take the alternator off and take it to be bench tested.

[Ron]

Yeah, his alternator had a bad diode/regulator in it.

Ahh...You should use a voltmeter for those tests (i.e. Use a probe for speed, a meter for accuracy) -- It is more than possible to have a draw that can make a bulb burn/glow, for example, but not enough to make that bulb and a probe's bulb burn at the same time, depending on the exact problem. If the bulb burns, there has to be measurable power on one or the other (terminal wire or terminal). But it seems that something has changed.

Yes, a bench test is the best way... If it passes and/or the light starts coming back on, or just for SOP, repeat the test from ground to the light/terminal with the key off using a volt meter.

[RedDMC]

Yes, very strange that I can't reproduce the symptom that started this thread. Now I am more concerned about the battery light growing increasingly brighter with the rpms increasing. It's like the engine is sucking the power right out of the system and making the light get really bright. Enough speculation. Bench test this weekend.

[Ron]

Yes, very strange that I can't reproduce the symptom that started this thread. Now I am more concerned about the battery light growing increasingly brighter with the rpms increasing. It's like the engine is sucking the power right out of the system and making the light get really bright. Enough speculation. Bench test this weekend.

That sounds like internal short(s) in the alternator (rectifier diodes or stator windings...it would be virtually fighting itself...and would blow the trio and/or regulator. I'd about bet money it is the problem now :-(

[RedDMC]

Hopefully I will get to yank it Saturday and take it to the autoparts store for a bench test. Ron, I appreciate all of your help. Hopefully, I'll get to meet you in person someday.

[Ron]

Hopefully I will get to yank it Saturday and take it to the autoparts store for a bench test. Ron, I appreciate all of your help. Hopefully, I'll get to meet you in person someday.
NP!

I think the next SEDOC meet (http://dmctalk.org/showthread.php?9580-Spring-SEDOC-Tech-amp-Social-Day-Saturday-May-31-2014-Buford-GA&p=140994#post140994) date is about to be carved in stone :biggrin:

[RedDMC]

It's official, alternator is shot. Who'da thought?

[RedDMC]

Thought I should check in with the updates. We had a friend in my Volkswagen club killed on the side of the interstate, next to his broken down Beetle. Needless to say, my attention has been diverted. The long and short of it is, I removed the alternator and took it to the autoparts store. They tested it and it made all kinds of noise on the test stand. The bearings were so bad that they stopped the test before it was done. I then took it to an alternator rebuild shop. They took it all apart and ended up replacing everything inside. The diodes were bad along with everything else that has been mentioned on this board. So, I haven't installed it back into the car yet, but it sounds like this may be the end of the saga.