Brake lights just barely staying on

[Robsmaze]

I’ve read a ton of posts about brake lights staying on at all times, but this one is a little weird. The brake lights function perfectly, I switched to LED bulbs and they are nice and bright. I redid the front and rear brakes and most of the brake lines during the restoration work this summer. They seem to work great, but they may be a little squishy (first Vanagon, I can’t tell what is normal) and I have considered bleeding them one more time.

But, I have 9 volts going to the brake lights all the time when the pedal is not pressed. It’s not enough that you can see the lights on during the day, it wasn’t even enough to see when parked near the garage with a few lights on at night. I just happened to have it parked away from the house and noticed two very dim red lights in back when I took the trash out. I have gone through the Bentley and its a pretty simple circuit. And when the brakes are pressed I get 12 volts and they turn on brightly.

Should I replace the two MC switches? Or is there some other culprit. I can imagine the switched completely failing, but I can’t figure out why I would get a partial voltage from them. I haven’t removed the instrument cluster yet, I figured I would ask here first.

‘87 Westy, 2WD.
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‘87 2WD 2.1L Westy
‘87 2WD 1.7L Diesel Doka (euro spec)

[jlrftype7]

There are a few posts on this from memory. One or both of the Brake switches faulting out and allowing current flow while you're out of the Vanagon and NOT pressing the brakes.
A simple meter check on the wires out , which sounds like you're already there with the 9 volt reading. Replaced faulty switch. As for partial voltage, the contacts are only allowing THAT much voltage and current through when the switch is in the normal Off Position instead of being totally open with no current flow at all.
You can also tap the switch with the handle of a screwdriver while you've got your meter on it and see if the voltage drops, increases, or jumps around, showing how the switch is behaving with vibration in the Off position.
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'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[crazyvwvanman]

There are 2 brake switches.
Just pull the wiring connector off one switch at a time to see if a switch is causing the problem.

Mark

[Robsmaze]

So, I popped the instrument cluster off and pulled the plugs from the brake switches off one by one and then BOTH of them and the very dim lights did brake lights didn’t turn off.

So, I measured voltage at the plugs. I have 0V on the red/yellow wire, but 5ish volts on the red black wire.

This is such a simple circuit. I can’t figure out how I’d be getting voltage. I must have some bad wiring in the red/black wire somewhere between the dash and the plug going into the tail light assembly?

Any ideas how to go forward?
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‘87 2WD 2.1L Westy
‘87 2WD 1.7L Diesel Doka (euro spec)

[RolandD]

I believe those switches have three prongs, not two. Is there another current track thru a brake fault circuit that you are not showing?

Roland

[Robsmaze]

I checked that. I have the two prong switches on the van.
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‘87 2WD 2.1L Westy
‘87 2WD 1.7L Diesel Doka (euro spec)

[ZsZ]

[fxr]

If you are measuring with a digital meter, that will be very high impedance, and may well show a voltage that is leaking through a large resistance. This can be a dirty connector, one or usually more dirty grounds, or corrosion on the bulb sockets.

Your LED lights also have relatively high impedance, and will light up with just a small current.

Put a more normal load across the wires and measure the current. The load can be any 12V incandescent (not LED) bulb. I bet the current is very, very low!
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Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300

[crazyvwvanman]

I would look for added trailer wiring or cruise control as possible sources of spurious voltage to the brake light wiring.

Mark