Battery drain issue...at my wits end. Any ideas?

[Broncojunkie]

Hey guys. This is a problem I'm having on my 88gt.

The battery drains over night. I've dealt with plenty of these battery drain issues, but this one really has me stumped. I went through the drill. Removed battery cable and hooked up a meter between the battery and the cable. Since I had the drivers door open, I removed the fuse for that circuit. I then proceeded to pull fuses one at a time. No matter what, I was showing just under 13 Volts (with a fully charged battery). I even pulled all of them at once (after taking a pic, so I could put all of them back where they were.) No drop in voltage whatsoever.

I then turned my attention to under the hood. I unplugged different things: alternator, wiper motor, distributor, etc. Again, no change.

So I decided to try something else. I went to the starter relay on the fender. On the hot side, I had the positive battery cable along with 4 other wires with ring terminals. I figured pretty much everything that doesn't run through the fuse box would go through this...using fusible links. With only the positive cable connected, there is no drain (or very little....less than 1v, iirc). If I touch any of the other 4 wires to the stud on the relay, the voltage drain goes right back up to 13(ish). My plan was to touch these one at a time until I found one that was causing the problem...but each one individually seems to be causing a ground issue.

Any ideas? I'm at a loss here.

[tonysilver82]

check you sunvisor lights and unplug the alternator

[JACook]

The meter is probably not the best tool for this job, especially if it's a digital meter. There are several
parasitic loads that will keep the meter displaying battery voltage, even when the actual current draw
is in the milliamp range. A test lamp won't be fooled so easily. Or, if your meter has a decent Amps
range, you might try that instead.

[Broncojunkie]

Both of the visor lights have been unplugged for 6 months or more. I tried to deal with this back before it went to the paint shop (who kept it for 6 months.) I also unplugged the alternator...both plugs.

[Broncojunkie]

The meter is probably not the best tool for this job, especially if it's a digital meter. There are several
parasitic loads that will keep the meter displaying battery voltage, even when the actual current draw
is in the milliamp range. A test lamp won't be fooled so easily. Or, if your meter has a decent Amps
range, you might try that instead.

I tried a test light, as well. My thought in using the meter was that it should show a partial drop in the case that there might be two different circuits grounded. And the meter does appear to respond to partial drops in voltage. I tested it with a battery charger turned on and again with only the battery. It went from around 14v down to about 12.7 or so.

[JACook]

The problem is, the meter can read full battery voltage through a load, whether it's large or small,
single or multiple. Something as simple as a keep-alive supply can look very much like a larger draw.
At the very least, I would use both the meter and test light in series, so you have some known load
in your test circuit. Any load worth worrying about will cause the light to at least glow.

[Broncojunkie]

The problem is, the meter can read full battery voltage through a load, whether it's large or small,
single or multiple. Something as simple as a keep-alive supply can look very much like a larger draw.
At the very least, I would use both the meter and test light in series, so you have some known load
in your test circuit. Any load worth worrying about will cause the light to at least glow.

I understand. You are saying that just because it is a 12v draw doesn't mean that it's enough amps to drain it...correct? Seems like I tried amps before, but I can try that again. I have had success in the past by using a test light and you can tell you found it when the light dims significantly. I'll try all that stuff in the morning and see if I have any luck.
Thanks

[84GT350CONV]

You either have an alternator or a voltage regulator problem. Typical Ford issue. I'd replace both at the same time as the voltage regulator doesn't cost that much. You will go crazy trying to isolate it as it is a slow drain affair. Believe me I've dealt with this more than once. Just replace those items and you should be fine. If not just return the parts but I'm 99% sure this will solve your issue. I've never done it but I also heard it's a blown diode on the bridge rectifier that's the main cause.

[JACook]

A blown diode does not cause battery drain. A shorted diode could, but that's not usually how alternator
diodes fail. A regulator could cause the problem, if it's electronic, and the driver transistor has a collector-
emitter short. That would cause the alternator field to be energized when it shouldn't be. That one's easy
to verify, just unplug the regulator. No need to swap any parts.

[Broncojunkie]

I did try unplugging the alternator. As a matter of fact, I had that problem with my 92 F150 a couple years ago. The way I found it was I just so happened to put my hand on the alternator and felt a little heat coming from the vr. I had been planning on doing a 3g swap anyway, so that fixed the issue. No such luck with this car. I do have a 3g alternator I'm planning to install, though. I don't like the problematic plug (fire hazard) on the old one. I think it's ok as long as the fuse link is still there, but I know people bypass them over the years. This one still has the fuse links in-tact, but I very well may put an e-fan in it some day.

[Broncojunkie]

Ok. Checked amp draw and with everything turned off, doors shut, etc., it appears it is somewhere between 8 and 18 mA. Is this enough of a parasitic drain to cause my issue? Or do you think the battery is bad? The battery is just a little over a year old and has spent most of its life in the car, but unhooked. It seems to hold a charge, but it may just not be holding much.

[grabbergreen84]

Can you try leaving the battery in another car? That will rule that out...

My first thought was a bad diode in the alternator...

Big stereo amplifier staying on?

[mustang22]

Had same issue. Turn out to be stereo (amplifier-subs) draining it.

[Broncojunkie]

Hey guys. Thanks for the suggestions. I just have a basic head unit and the only speakers currently in the car are the dash speakers (which sound awesome, lol). I've had the head unit out of the car while I'm working on the interior, anyway, and it still appears to be draining. I've left the battery unhooked for about 3 days now, and it seems to be holding a charge just fine. I believe while it's unhooked, I'll take it somewhere and have it checked just to rule that out. I am headed to the parts store today, anyway.

I read something online that said anything less than 50 mA drain should be ok. Mine appears to be a maximum of 20 or so. Not sure how accurate the meter is, of course.

[Broncojunkie]

I just realized I forgot to go back and update this thread. A new alternator fixed her right up. As it turns out, a short inside the alternator was causing the battery drain, although, it would only do it on occasion and even tested good at the parts store (bench test). My guess is that it would short sometimes, depending on where it came to rest in its rotation.

[Haystack]

As the brushes get hot they fail. I had to have mine tested 3x before it failed.

With a battery, a 1 amp (1000mah) drain would take 20-80 hours to fully drain the battery, depending on battery size and condition. 8-18ma is probably within the tolerances of the meter readings. A single 1156 bulb pulls one amp, for reference. Just an FYI.

[83gtstang]

Awesome, it's always best to replace the vr along with the alternator if you haven't already and possibly the battery too. Just did this to my Escort, chased my tail, just to realize the battery was struggling to keep a charge. I guess a free so many drains, it just messed it up.