1988 928S4 Auto RHD
Hi guys I’m not good at using the search feature so thought someone may be able to answer a quick battery drain question I’ve got.

I have 280 milli Amp drain on the battery. Battery fully charged, all doors and windows shut.
i started pulling the fuses and the only one that made any difference was fuse 24 which on my fuse chart is for the interior lights and hatch release start. When I pull this fuse the drain drops from 280 MA to 140 MA.
so I obviously have a fault on the lighting circuit which I belief is very common but do I have another issue that’s not identified by pulling the fuses?
I think battery drain should be less than 50MA.
any ideas where is should start please.
I unplugged the rear hatch light socket and it made no difference. I pulled wires out of the dome light and no difference.
help please
thank you

 

I suggest to disconnect the ground connector at the hatch latch and leave it disconnected,
then the interior lights wont be activated nor will the alarm switch be triggered.
Remove the rt parcel tray and the upper CE panel cover ,
roll down the rt window then close the door.
Use an IR gun to find any warm relays, by leaning in through the window,
pay attention to the HVAC and the X bus and interior lights/ window relays in particular .

NOTE check all the relays for the proper part number and position,
NOTE relays can be damaged by water filling them corroded pins are a clue ,
OR running the car with a depleted battery will also damage the relays,
as they wont get strong closing voltage ,
this lets the contacts get dirty, then they wont pass voltage then the contacts will get hot.

 

The drain should be about 30mA.

I had a similar problem- it had something to do with the rear hatch release so I disconnected the wiring - problem solved.
One of these days I will investigate the problem but undoing the hatch with the keys is not what I would call a hardship

 

Thank you I’ll try that

 

thank you

 

Did you try pulling relays as well? Those can often fail and be the cause of battery drains.

 

no I haven’t tried that. Some of them are new but will check, thank you

 

What is the state of the interior lights? Do they work correctly? do you have them all turned off?

Alan

 

Check the bulbs under the door latches (the ones you can only see with the door open). Sometimes they stay lit even with the door closed.

Rich

 

thanks will do

 

hi Alan. The fault was present when I first bought the car about a year ago. I’m sure the lights were working then. I took the bulbs out then. When I put a couple back in ie the tailgate bulb and the dome light bulb neither appears to be working. I haven’t tried putting the bulb back in on the three way adjusting light in the door by your knee. I don’t think I removed the bulbs in the red end door lights but haven’t checked them yet.
people seem to say these lights could well be my problem.
The fuse in the board is ok.

 

This will only be the case if there is a fault on the interior light relay or its pin switches. Often all the interior lights get switched off (from door controlled mode) but this doesn't stop the door end lights from saying on. Open one door (night time is best) the door end light should come on, If it doesn't It's highly likely one door end bulb is out so then try the other door (on its own). When it comes on - hold in the door pin switch - after ~15 sec it should go out - if it doesn't this is your always on load. From the value I'd expect one bulb is burned out already from always being on.

Alan

 

Thanks Alan that’s just what I needed. I’ll check this out on Monday when I can get back on the car.👍

 

to see the if the bulbs are working simply roll down the windows look inside the door slot ,
you will see if the bulbs are lit with the door closed or open.
NOTE usually the wire harness becomes a water path that fills up the boot ,
then inside the the light housing just rusts away from being submerged.
I set the lamp housing then add some silicone sealant to the back of
the harness and the boot this stops water migration

 

thanks