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Brake light switch stuck ON, nearly stranded.
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fxr
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Joined: December 07, 2014
Posts: 1516
Location: Bay area CA
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PostPosted: Sat Jul 30, 2016 11:43 am    Post subject: Brake light switch stuck ON, nearly stranded. Reply with quote

In the hope this may help someone else with a pre-85 Vanagon, here's a tale of the failure of a three-pronged brake light switch.

We were coming back from a trip to the San Juan Islands from CA, when the brake warning light started flickering on. In a way we were lucky we had the older three-prong switch arrangement, as at least this did give a clue, even if I wasn't fully cognisant of the implications at the time. We were also very lucky that this intermittent fault wasn't showing when we camped for our last night on the road. The van seemed to run OK, and I at first assumed it was a dodgy handbrake switch.

The circuit of the three-pronged switches in the earlier Vanagons was designed to give an indication of the failure of one of the two separate brake hydraulic systems. If a hydraulic circuit had failed then when braking the brake warning light should illuminate. If the light comes on when you're NOT braking - it means one of the switches has failed closed, and the brake light is stuck on. Well, I know that now...

In our case, we were carrying a Vespa scooter on a rack with its own brake lights on the back - this meant a total extra current drain of ~7A, and with four extra large 12V fans running inside (it got to over 112F through Redding, no A/C) and the headlights on (we leave them permanently on) the alternator had a hard time keeping up. After the last gas stop the engine barely turned over.

It didn't help diagnosis that I couldn't monitor battery volts while we were driving as Mrs fxr had shoved a 12V ciggie connector in too hard the day before, breaking the back of the socket and blowing both main and aux accessory fuses - she had switched across between batteries when the power first failed for her. The fuses in my set-up are under the driver's seat with the Aux battery, and not easily accessible without removing the driver's seat. I was leaving the task until we got home.

We did make it home thank goodness, and after I changed out the accessory fuses I saw that the main battery was down to 11.3V. I disconnected it, charged it up, then checked for parasitic current. Yikes! 7A! This with the van shut down!

A visual inspection of the handbrake switch showed that couldn't possibly be the problem, and the Bentley circuit diagram confirmed it as the handbrake switch only gets power with ignition on. The only possible fault was that one of the brake light switches had failed ON, and with the brake light 12V feed permanently tied to the battery via fuse S8 this could lead to a drained battery in very short order. It would be quite easy not to notice the brake lights were left on when leaving the van, and vans with the later two-prong switches would have given no other visual warning of the fault.

I've ordered new switches of course, and in the meantime have left the offending switch disconnected.

If I had a later van, I'd be thinking of added a brake light tally LED to the instrument cluster.

I hope this tale can save some grief for someone down the line. Wink
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Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300
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Paulbeard
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Joined: July 10, 2015
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Location: Seattle
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PostPosted: Sat Aug 05, 2017 1:12 pm    Post subject: Re: Brake light switch stuck ON, nearly stranded. Reply with quote

I just had this happen but in my case it just something to do with the multipin connector. I had been doing some mucking about work on the wiring and found that the handbrake light was staying on and flickering with the turn signals. Opened up the binnacle, wiggled the MPC to make sure it was seated and that seems to have solved it.
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Currently -> Frida: 87 Tizian Red (mostly) Vanagon GL Westfalia w/ 2.0L ABA conversion
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fishgo
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Joined: June 21, 2018
Posts: 106
Location: Madison, WI
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PostPosted: Thu May 09, 2019 7:04 pm    Post subject: Re: Brake light switch stuck ON, nearly stranded. Reply with quote

fxr wrote:
In the hope this may help someone else with a pre-85 Vanagon, here's a tale of the failure of a three-pronged brake light switch.

We were coming back from a trip to the San Juan Islands from CA, when the brake warning light started flickering on. In a way we were lucky we had the older three-prong switch arrangement, as at least this did give a clue, even if I wasn't fully cognisant of the implications at the time. We were also very lucky that this intermittent fault wasn't showing when we camped for our last night on the road. The van seemed to run OK, and I at first assumed it was a dodgy handbrake switch.

The circuit of the three-pronged switches in the earlier Vanagons was designed to give an indication of the failure of one of the two separate brake hydraulic systems. If a hydraulic circuit had failed then when braking the brake warning light should illuminate. If the light comes on when you're NOT braking - it means one of the switches has failed closed, and the brake light is stuck on. Well, I know that now...

In our case, we were carrying a Vespa scooter on a rack with its own brake lights on the back - this meant a total extra current drain of ~7A, and with four extra large 12V fans running inside (it got to over 112F through Redding, no A/C) and the headlights on (we leave them permanently on) the alternator had a hard time keeping up. After the last gas stop the engine barely turned over.

It didn't help diagnosis that I couldn't monitor battery volts while we were driving as Mrs fxr had shoved a 12V ciggie connector in too hard the day before, breaking the back of the socket and blowing both main and aux accessory fuses - she had switched across between batteries when the power first failed for her. The fuses in my set-up are under the driver's seat with the Aux battery, and not easily accessible without removing the driver's seat. I was leaving the task until we got home.

We did make it home thank goodness, and after I changed out the accessory fuses I saw that the main battery was down to 11.3V. I disconnected it, charged it up, then checked for parasitic current. Yikes! 7A! This with the van shut down!

A visual inspection of the handbrake switch showed that couldn't possibly be the problem, and the Bentley circuit diagram confirmed it as the handbrake switch only gets power with ignition on. The only possible fault was that one of the brake light switches had failed ON, and with the brake light 12V feed permanently tied to the battery via fuse S8 this could lead to a drained battery in very short order. It would be quite easy not to notice the brake lights were left on when leaving the van, and vans with the later two-prong switches would have given no other visual warning of the fault.

I've ordered new switches of course, and in the meantime have left the offending switch disconnected.

If I had a later van, I'd be thinking of added a brake light tally LED to the instrument cluster.

I hope this tale can save some grief for someone down the line. Wink


I've just be alerted that this may be my problem from today. I'll check it out. https://www.thesamba.com/vw/forum/viewtopic.php?p=9071590#9071590
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