T5.1 Parasitic Drain Fuse SB12

C

charlie16161

Messages
14
Location
UK
Vehicle
T7 California Ocean 4 Motion
I've got a parasitic drain on my T5.1 and eventually established its on fuse SB12 which is the light switch circuit. I've confirmed its this circuit by pulling the fuse. Problem I have now is establishing what actually runs on this circuit. I've removed the switch itself and the terminals all look clean. Retested with the switch out and the drain is still there.
Does anybody out there know what else runs on this circuit?
Thanks
 
charlie16161 said:
I've got a parasitic drain on my T5.1 and eventually established its on fuse SB12 which is the light switch circuit. I've confirmed its this circuit by pulling the fuse. Problem I have now is establishing what actually runs on this circuit. I've removed the switch itself and the terminals all look clean. Retested with the switch out and the drain is still there.
Does anybody out there know what else runs on this circuit?
Thanks
Click to expand...
Fuse for Lighting switch E1

Possibly Headlight switch. Check Parking lights.

The "light switch E1" on a VW Transporter likely refers to the headlight switch. Specifically, it could be the switch that controls the vehicle's headlights and potentially other exterior lights.The "E1" designation is likely an internal code used by Volkswagen for this specific component.

Here's a more detailed breakdown:
  • Headlight Switch:
    The primary function of the E1 switch is to allow the driver to select different headlight modes, such as parking lights, low beams, high beams, and potentially fog lights.

  • "E1" Designation:
    In Volkswagen's internal system, components are often assigned codes. "E1" is likely the code for the headlight switch.

  • Potential Issues:
    A faulty headlight switch can lead to various problems, including headlights not working, flickering, or only working in certain modes.

  • Ross-Tech Wiki Reference:
    The Ross-Tech Wiki mentions "Light Switch (E1)" in relation to fault codes and potential issues with the parking light status lamp and self-dimming rearview mirror.
 
1755525087940.png
Starter for 10, so any of those outputs from the switch that SB12 feeds.
 
Starts from page 65

VW Transporter T5 (From August 2009) – Wiring Diagrams

VW Transporter T5 (From August 2009) - Wiring Diagrams INDEX: 001 - Basic equipment 002 - Convenience system 003 - Anti-lock brake system (ABS) with electronic stabilisation program (ESP) 004 - Climatronic 005 - Headlights with halogen bulbs (H7) , (8K3),(8K8) 006 - Preparation for mobile...
fixmycarinfo.com
 
Thanks for your replies - I'm not brilliant with electrics but a multi meter test showed a draw of .13 milliamps so I did the test of pulling the fuses individually to identify it then cross checked the fuse directly and they both point towards this as the culprit. For the time being I've pulled the fuse and the battery power drop has stopped but obvs cant drive like this! All the lights are working ok and again I can confirm its the correct circuit as when the fuse is out the light switch doesnt work and the dash panel isn't illuminated. I suppose its just a case of trying to identify and test whatever is in this circuit. Any ideas on what I might be looking for? I dont really want to start pulling cables as that sort of thing is above my pay grade!
 
Just to add to that - I've bought one of those Bluetooth battery testers from Amazon - before I pulled fuse 12 it was showing the battery on less than 50% and 11.8v. Since I've pulled it (and it hasnt been on charge nor have I started the engine) its improved to 74% and 12.6v.
 
Are you testing this with the van fully asleep?
 
Do you leave the van with the light switch set to AUTO or do you fully switch it OFF? I've seen this be the cause of parasitic drain before. Something to do with a bad photo cell.
May be worth trying both scenarios to see if there is a change?
 
sidepod said:
Do you leave the van with the light switch set to AUTO or do you fully switch it OFF? I've seen this be the cause of parasitic drain before. Something to do with a bad photo cell.
May be worth trying both scenarios to see if there is a change?
Click to expand...
Thanks for your reply again. I dont have an AUTO setting. The only settings are for OFF Sidelight and Dipped with the Fog lights further down on the left. Just checking though. I removed and disconnected the switch and it made no difference so I assume can I eliminate the actual switch as the cause?
 
If you removed the switch and saw no difference then you can discount anything down stream of that.
Are you sure it’s that fuse?

Apologies if I’m telling you something you know but, you do have to let the van go to sleep before doing any tests.
This means key out and any doors left open need to have the latches sprung closed to fool the van they’re closed. This goes for the bonnet too.
Leave it alone for 15 mins and it should be asleep.
If any modules are still awake they will fool you and give a high draw. As ever, YouTube is your friend.
 
sidepod said:
If you removed the switch and saw no difference then you can discount anything down stream of that.
Are you sure it’s that fuse?

Apologies if I’m telling you something you know but, you do have to let the van go to sleep before doing any tests.
This means key out and any doors left open need to have the latches sprung closed to fool the van they’re closed. This goes for the bonnet too.
Leave it alone for 15 mins and it should be asleep.
If any modules are still awake they will fool you and give a high draw. As ever, YouTube is your friend.
Click to expand...
Thanks Sidepod. I'm fairly sure the Vans asleep and agree with you - there are plenty if YouTube vids out there on the subject. I've locked all the doors and used a screwdiver to close the bonnet catch then waited. So far as the fuse is concerned I'm sure its this one. I did the test by individually pulling the fuses until the drain dropped to Zero and identified it as being fuse 12 then with all the fuses in and battery attached double checked by testing the fuses individually with the prongs from the multimeter. All the other fuses drop to Zero but fuse 12v registers 130 mA. So is it just the light switch runs off this fuse?
 
Ok good, sounds like you’re on it.
As far as the wiring diagram shows, it’s only the main light switch.

Are you sure there are no after market mods to the van that may have used this supply?

It may be worth throwing £7 at Erwin for an hour and downloading the exact circuit diagram for your VIN number, just to be sure.

So if you removed the switch then the problem is between the main power distribution box and the switch.
Try removing the fuse and running a separate power supply directly from battery to the light switch then see if that solves it. At least then you’ve isolated everything downstream of the fuse.
 
Have you scanned the van with VCDS? There may be a fault present that could help?
 
Thanks again and good suggestions. I dont have a VCDS tool. Only invested in a basic engine scanning tool so might be a idea to buy one. Its due a service on Thursday so will ask the garage if they can do a scan. Didnt want them investigating the fault as electrical diagnostic can get time consuming and expensive. Mind you Ive already done a lot of the leg work already so it could be worth me asking their opinion.
 
Interesting you say about aftermarket mods. Its a conversion by 8 Ball so professionally done however I was working on it a few months ago as I noticed it has a reverse camera in the back number plate which is wired to the rear lights but doesnt work. I think its not part of the conversion but more like something done either before or after. I gave up on it after doing a bit of googling and opinion was the standard headunit doesnt support a reverse camera. I wonder if this could have anything to do with it
 
I mentioned I'd pulled fuse 12 yesterday. I left it out and just looking at my app and the battery is on 95% and 12.6. So no drop at all. I'm going to do another multimeter test again later to see what the draw is with the fuse out so will post and let you know. If its Zero I'll put the fuse back and monitor the battery for a day again.
Once again thank you so much for your time and advice
 
charlie16161 said:
Thanks again and good suggestions. I dont have a VCDS tool. Only invested in a basic engine scanning tool so might be a idea to buy one. Its due a service on Thursday so will ask the garage if they can do a scan. Didnt want them investigating the fault as electrical diagnostic can get time consuming and expensive. Mind you Ive already done a lot of the leg work already so it could be worth me asking their opinion.
Click to expand...
just ask them to do a full Auto Scan, save to the log file and email it to you.
 
charlie16161 said:
Its a conversion by 8 Ball so professionally done however
Click to expand...
My money is on a crappy little Chinese black box buried somewhere originally fitted for some footwell/coming home/drl lighting timer or similar.
 
Actually now you come to mention crappy little black box i have got this near the window on lhs of dash. Always assumed it was for the Sat Nav

20250819_091338.jpg
 
charlie16161 said:
I mentioned I'd pulled fuse 12 yesterday. I left it out and just looking at my app and the battery is on 95% and 12.6. So no drop at all. I'm going to do another multimeter test again later to see what the draw is with the fuse out so will post and let you know. If its Zero I'll put the fuse back and monitor the battery for a day again.
Once again thank you so much for your time and advice
Click to expand...
According to @sidepod wiring diagram there are 2 fused supplies to the switch SB12 and SB22.
What happens if you remove SB22 but not SB12?
 
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