thepurpleblob

1986 Euro S2. More trouble...

Some background - I used to run a car audio / security company and so kinda know what I'm doing and have decent test equipment.

The problem. The car drains the battery from a full charge to just about nothing overnight.

Info / what I have done (in no particular order)
- I have tried two good batteries (both check out with a tester)
- I have checked with an ammeter in the battery earth lead. The current varies but it's the order of a few tens of milliamps. Nothing to account for an overnight drain
- I've checked for current drop across the fuses (reliable method with good milliammeter). Found nothing. Zero over everything.
- Checked the alternator (mostly for something to do). Stripped, cleaned, diodes tested, regulator replaces (as brushes were almost gone). All fine

So, I've found nothing to account for it. When I'm there it's not draining.

Any ideas are much appreciated.

gazfish

Maybe it was a dream, but didn’t you find the problem a while ago on another post?

thepurpleblob

You're right. I'd completely forgotten that I'd posted about it (old age). I've been busy with work and it got sidelined.

Yeh - I've got back to it over the last couple of days and I'm getting increasingly frustrated as I'm just not seeing the drain.

Mrmerlin

get and IR gun ,
charge the battery drive the car for 5 miles,
park it.
NOTE with the passenger side parcel tray removed and the CE panel cover removed
and the right pax window down.

Wait for 10 mins then reach through the window with the IR gun and shoot your panel,
your looking for warm relays,
any that are warm should be investigated and replaced.
NOTE also disconnect thewhite 2 pin pin switch connector for the hatch it has 2 brown / white stripe wires at the hatch latch area,
this is a switch that will run your door lamps without you knowing they are on .
NOTE look inside the doors to verify the rear edge lamps are out when the doors are closed

FredR

Is your 928 locked overnight? Draining overnight is a hell of a current draw- 5 amps? You are looking for circa 30 mA.

If so you need to test in the locked and armed state and that takes a few seconds after arming but that is on my GTS.

Presumably your meter is DC capable- given your background it is a certainty but...?

thepurpleblob

None of the interior lights work... I've been too lazy to fix them so I doubt it's that. The red lights in the doors definitely don't. However, I shall re-check. I'm very reluctant to take the door cards off if I don't have to.

I checked the relays before and found nothing but I'll do it again. It would make sense if a relay had gone intermittent. It would have to be switching in by itself only when I'm not there. Which while not impossible, is a bit irritating.

mkhargrove

if you have a full charge, do you have a spark if you disconnect a batter cable and then tap the connector against the battery post? if it's draining from the circuit that quickly, you would see a spark. BUT....I would not be surprised if your battery is toast. when they have bad plates they can have almost no capacity so that they will charge to 12+ volts but then you turn lights on for 1 minute and the battery is drained. and, the battery can have it's own internal short, again giving the appearance of looking normal by charging to 12 volts, but draining themselves back down pretty quickly without even being connected


do you have another vehicle that you can pull the battery from and see if it drains as quickly?

thepurpleblob

There is a spark when I connect it but only the first time. I assume that this is some capacitors somewhere charging up. Just to reiterate, I have a decent battery tester and that claims that more than one battery is fine. The battery makes no difference. Also, I cannot detect a large discharge with a multimeter.

All of which leads me to think that I'm either doing something stupid, it's an intermittent fault, or both.

Mrmerlin

NOTE not only are the lights on for the doors and interior,
also a relay is energized on the CE panel,
so even if the lights dont work that circuit is ON.
NOTE mis wired interior lights can cause a battery drain.
At this point I suggest to fix all of the door and interior lamps,
replace the 2 of the overhead units with Jetta lamps the aft hatch lamp,
I would disconnect and heat shrink the wires. .

You can buy new door edge lamp housings with new bulbs and sneak them out of the doors without taking off the door panels.

Broccoli

Headlight motor?

I had an intermittent battery overnight drain problem and this was the cause. The wheel sensor attached to the motor that senses the light position had enough corrosion to keep the circuit closed. It was obvious because the motor got quite warm.

1986.5 928S

thepurpleblob

Ok, but there isn't a circuit if the bulbs aren't working so where is the electricity going?

Ahh... I missed your point about a relay. So if, for example, the hatch is open (or it "thinks" it is) are you saying that this energises a relay? I need to go and stare at the circuit diagram.

FredR

When the car is in sleep mode all relays are de-energised however if a relay is for instance stuck in the powered condition logic says current may be flowing through the thing and I2R losses will heat it up some thus a warm relay relative to the rest of them signifies a logical circuit for investigation.

Mrmerlin

Yes the relay is energized possibly from a light fixture with the ground and the switched ground reversed,
or a switched ground broken wire thats shorted to ground , or a bad hatch pin switch.

That said please follow my instructions for finding a warm relay ,
then report your findings,
and then you can be instructed on what circuits to follow.

thepurpleblob

Sure - I'm getting to that just as soon as I have a charged battery!

I'm also going to have another close look at the wiring diagrams

mkhargrove

just curious....how old is your engine harness? any chance you have some insulation missing around the 14 pin connector?

check amperage across each fuse bracket....?