Brake lamp switch fuse keeps blowing.... simples you would think:)

[WillVito]

Need help......

So a little history....
Bought van 9 months ago......was told at time it had had some elec faults but fixed and all good so bought van
About a month ago had to do a low speed (prob 5mph or less)emergency stop after my GF screamed so loud it scared the hell out of me to the point where I slammed on so hard I thought id snapped the brake pedal off....ABS engaged. The pedestrian I was supposedly going to run over didn't even notice.... I was apparently looking out of the window at something....it has been known

Anyway within 24 hrs of this I got ASR/BAS symbol and ESP lit up......
After initial panic and a few carefully chosen words realized that it drove fine with no issue so no big deal.... then got a blown bulb symbol lit up so thought best check it all out. At this point I realized I had no rear brake lights...none

So it begins

Discovered that No3 fuse (5 amp Brake lamp switch) in SRB had blown so replaced. Checked out all front and rear lights. I replaced a blown headlight bulb and checked all rear bulbs and sockets all good.....decided to replace both rear indicator bulbs as the amber was rubbing off.

Started..... all good with all no warning symbols

Over the past 4 weeks the same fuse has been constantly blowing all rear brake lights working to all rear brake lights not working) It started of by getting a few days out of a fuse to the point where it blows almost immediately upon ignition now

During this time ive had the Brake lamp switch out. Continuity Tested it comparing against a new one and it was fine. Even disassembled to see if I could see something sus.
Checked out adjustable travel on switch and reinstalled.....
Ive tried to isolate the problem by disconnecting rear clusters and leds one by one and reconnecting. This has sometimes worked for up to half hour of diving then fuse blows again.

where do I go from here......could it be the relays? or SAM?

please help

 

[silver1011]

Weird. Have the ASR/BAS and ESP lights been lit up all this time?

If not, how did you clear them?

Have you had the van scanned for fault codes?

 

[WillVito]

Over the past 3-4 weeks the ASR BAS ESP have been out whilst the fuse was stil good but as soon as fuse went they came back on. Just kept on replacing fuses to buy me time but this has now decreased to point where most of the time it blows a fuse on ignition. I can however get the brake lights working for a short time like this afternoon. I plugged the rear leds in again. Went down the hill 800yds braking fine (no warning lights) then turned corner over bridge and warning lights lit again. Fuse blown.

I looked through some paper work and found a receipt from a merc dealership

It state customer has had 3 switch replaced at non dealership garage and still keep blowing fuse and no brake lights.

It then stated there was a fault with the switch a new switch had been installed. stars was plugged in and reset codes or something. oh and they also installed correct fuse...think someone had put in higher amp fuse to see if thus helped...

The owner then sold it to me and its been ok for about 8 months....it seems to be up to its old tricks......

Have not had codes read again but suspect it will come up with faulty brake lamp switch code again.

Anyway have not had codes read yet.....

what next?

 

[silver1011]

I think reading the fault codes with STAR might help, the fuse is blowing in an effort to protect the electrical system, so I think the brake light / pedal switch, whilst a good logical starting point, is a red herring, especially given that it seems to have already been replaced several times, likely ruling out a duff batch of switches.

You mention "rear LED's". I didn't think the model / year of Vito in your profile picture has any LED's in the rear light clusters?

Could it be that the previous owner has retrofitted some LED's which might be causing the issue?

Mercedes Vito Rear Lights

• silver1011
• May 3, 2019

 

[WillVito]

Its got high level strip brske light......looks very much factory fitted.

 

[silver1011]

You're right, the high level brake light is LED...

Vito LED High Level Brake Light

• silver1011
• May 3, 2019

I'm at a loss then. Sounds like getting the van booked into a reputable auto electrical specialist is going to be the best route to a permanent fix?

 

[WillVito]

Think so.......Had mate look at it at local garage but they just have not got the time to spend on it.

They gave me a number of an Auto electrician but he wont work on Mercs as there a pain he says.

So will keep trying to find someone that willing....if not it might have to be the dealers as last resort.

Looked at buying star but too expensive....

Do you know if I unplug the SAM module can I just put a replacement in with out the need for stars?

Thanks

 

[WillVito]

Update.

I found this other thread that has helped

Brake light fuse blows when pedal NOT pressed! (pics)

So I ve disconnected the Black/Yellow wire from the Switch...Ive got brake lights back and fuse is holding up

ASR/BAS ESP warning lights are stil lit up.

So guessing its a short somewhere on this wire yet suspect it might be not that simple.....

 

[Codger49]

As you need 30 posts to send a personal message, I had thought of sending a PM to Vito V6 to see if he had any success with his fault, but it seems he hasn't been seen since August 2017.

Will try anyway.

 

[WillVito]

Thanks so much.
appreciated.
Not sure if you stil have any of the info you emailed vito V6 but if you do it would really help.

Thanks

 

[Codger49]

Funnily enough, I keep an email archive.

These are the two pdfs I sent him.

Remembering there were some differences in VITO wiring over time and versions, it may be advisable to post up your VIN, so I can extract the correct diagrams from WIS for your vehicle.

 

[WillVito]

Nice one thanks.....I will get the VIN first thing tomorrow morning.

Thanks again

 

[WillVito]

VIN No WDF63960123556534

 

[Codger49]

As far as I can tell, the circuit diagram I posted yesterday, PE42.45-S-2000-97vb, applies to your vehicle.

I.e it is for a 639.601 model 115 after chassis no 195057, with a 646.980 engine and 716.652 transmission fitted with option BB3 (ESP), XZ0 (Model Generation 0), but not fitted with option CL9 (Eco power steering pump), nor MA0 (60 kW E-cell).

 

[WillVito]

Nice one. Thanks

 

[tron]

Remove the bulbs. fit a 2Amp fuse. If the fuse blows on power up you have a wire grounding out as the vehicle has had all along, I suspect.

 

[WillVito]

Thanks Will try this out. Have not had much time to test wires...but will report back when I do....

 

[mdj101]

Hi There.

did you ever get to the bottom of this?

I’m having the exact same issues. Fuse started blowing intermittently over a year ago, then gradually got worse until it blew as soon as you replaced it and hit the brake pedal.

i disconnected all the real light clusters and high level lights and it would still do it. Metered the output and couldn’t find a short anywhere. Replaced the fuse board this morning but still blowing.

next is to disconnect the abs pump... but any heads up would be great.

 

[AnttiR]

Hello!

I have same problem with vito 115 2010.
Anyone have solution for this problem?
Brakelight switch fuse (5A number 3) blows when i press the brakepedal. Switch is new, not original but same problem with original switch.

 

[Larkone]

Hello!

I have same problem with vito 115 2010.
Anyone have solution for this problem?
Brakelight switch fuse (5A number 3) blows when i press the brakepedal. Switch is new, not original but same problem with original switch.

WillVito​

New Member · 45 · From Northwich
Joined Apr 26, 2019
Last seen May 7, 2019