SOLVED: Parasitic Draw if Cabin Light Switch is in auto mode

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matreyia
Posts: 64
Joined: Dec 22, 2021 1:05 AM
Location: Houston

SOLVED: Parasitic Draw if Cabin Light Switch is in auto mode

Post by matreyia »

Hi Everyone,
So I been reading on this site about parasitic draws and haven't found anyone who has the problem similar to my issue. The battery goes dead overnight if I set the interior cabin light switch on the dash board to the centered setting - the setting where the lights turn on only when the doors are open and turn off when the doors are closed.

If I turn the switch to totally OFF position, there is no draw at all and she starts up lickety split. Also, I can hear a slight buzzing sound if I plug in the interior air quality vacuum hose electrical connector located in the left side of the driver on the trim covering under the steering column. So at first I thought it was this and I disconnected that air sensor. However, it will still zap the new battery if I set the cabin light switch to the normal automatic setting.

Any ideas and suggestions appreciated. I want to try to check the trunk and glove box light also but don't really know how to do that with those lids closed. Maybe a bore scope?

Thanks in advance Everyone.

VT
Last edited by matreyia on Jul 17, 2022 4:51 PM, edited 1 time in total.
beaseac
Posts: 14
Joined: Apr 25, 2021 3:32 PM
Location: South Carolina

Re: Parasitic Draw if Cabin Light Switch is in auto mode

Post by beaseac »

I've also experienced this in my 1988 528e... I haven't had a chance to look into it so I just keep it in the off position for now.

<edit>
I should note that it usually doesn't die overnight but within a few days if I don't drive it.
matreyia
Posts: 64
Joined: Dec 22, 2021 1:05 AM
Location: Houston

Re: Parasitic Draw if Cabin Light Switch is in auto mode

Post by matreyia »

Good to know I'm not the only one. I guess I will have to get a borescope...need one Anyway.
///M
Posts: 74
Joined: Apr 17, 2009 11:21 PM

Re: Parasitic Draw if Cabin Light Switch is in auto mode

Post by ///M »

If your car has the interior light delay then it could be the problem. They can go faulty and cause the current drain. On a RHD car it is on the right hand side of the car under the dash. Part no. 61 31 1 373 974 or 61 31 1 373 975. Tall black relay. If you remove it and check if there is still a current drain.
matreyia
Posts: 64
Joined: Dec 22, 2021 1:05 AM
Location: Houston

Re: Parasitic Draw if Cabin Light Switch is in auto mode

Post by matreyia »

Good to know. I will definitely Check this. Thanks!
///M
Posts: 74
Joined: Apr 17, 2009 11:21 PM

Re: Parasitic Draw if Cabin Light Switch is in auto mode

Post by ///M »

To check the boot light a small child is useful but I think nowadays that is probably not allowed!
If your phone can record video then put it on record and place in the boot or glove box to see if the light goes out.
matreyia
Posts: 64
Joined: Dec 22, 2021 1:05 AM
Location: Houston

Re: Parasitic Draw if Cabin Light Switch is in auto mode

Post by matreyia »

Oh now I feel stupid. That's a great idea. Thanks for the suggestion!
beaseac
Posts: 14
Joined: Apr 25, 2021 3:32 PM
Location: South Carolina

Re: Parasitic Draw if Cabin Light Switch is in auto mode

Post by beaseac »

///M wrote: Jun 25, 2022 5:05 AM If your car has the interior light delay then it could be the problem. They can go faulty and cause the current drain. On a RHD car it is on the right hand side of the car under the dash. Part no. 61 31 1 373 974 or 61 31 1 373 975. Tall black relay. If you remove it and check if there is still a current drain.
Thanks for this! I was wondering where this relay might be... in my Alfa Romeo I used a jumper to bypass the relay as it quit working long ago.
jayjaya29
Posts: 188
Joined: Jul 30, 2014 12:53 AM
Location: Atlanta, GA

Re: Parasitic Draw if Cabin Light Switch is in auto mode

Post by jayjaya29 »

Just messed with my interior light relay. Found 5 cracked solder joints. Inspect yours closely or just bypass it.
matreyia
Posts: 64
Joined: Dec 22, 2021 1:05 AM
Location: Houston

SOLVED: Re: Parasitic Draw if Cabin Light Switch is in auto mode

Post by matreyia »

Ok, if you got a parasitic draw and you replaced all your switches and all is in order... test your alternator. Turns out the alternator the vendor recommended was incorrect and had a rubber bushing isolating it from the ground to the chassis and thus caused the alternator not to charge AND the battery to drain when the car was both running or not running.

The incorrect alternator was fine, it just didn't have a negative chassis mount like the 1988 one does. Replaced it with a proper unit and battery is solid, after four days of testing with the switch in automatic door light mode.
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: SOLVED: Re: Parasitic Draw if Cabin Light Switch is in auto mode

Post by Mike W. »

matreyia wrote: Jul 17, 2022 4:50 PM
The incorrect alternator was fine, it just didn't have a negative chassis mount like the 1988 one does. Replaced it with a proper unit and battery is solid, after four days of testing with the switch in automatic door light mode.
Ah yes, sometimes the simple stuff gets you, I know I've been bitten before. :facepalm: On the alt, all it would have needed is a ~#8 ground cable between the body of the alternator, on one of the posts sticking out, to ground and it would have worked just fine.
matreyia
Posts: 64
Joined: Dec 22, 2021 1:05 AM
Location: Houston

Re: SOLVED: Parasitic Draw if Cabin Light Switch is in auto mode

Post by matreyia »

Yeah, there was a negative bolt and nut on the alternator but I decided to trade for the proper model to keep wires to minimum and fidelity to the year.
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