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72VWSB
Samba Member
Joined: August 06, 2018
Posts: 707
Location: New Mexico
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 Posted: Tue Jul 20, 2021 7:59 pm Post subject: Brake lights on 72 SB? |
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I seem to have the passenger brake light not lighting up on my 72 SB. However, they both light up when I turn on my emergency flashers... Anyone know where I would look to fix this?
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72 VW Super Beetle |
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Cusser
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Joined: October 02, 2006
Posts: 31378
Location: Hot Arizona
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bomberbob
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Joined: May 17, 2015
Posts: 688
Location: Iowa
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| Posted: Wed Jul 21, 2021 4:46 am Post subject: Re: Brake lights on 72 SB? |
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And the bulb is good, yes?
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1968 Beetle (storage)
1990 Jetta GLI megasquirted, burning E85 (currently in heavy maintenance)
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72VWSB
Samba Member
Joined: August 06, 2018
Posts: 707
Location: New Mexico
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| Posted: Thu Jul 22, 2021 7:24 am Post subject: Re: Brake lights on 72 SB? |
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Sorry it took me so long to get back to this thread but it seems everything breaks at the same time!
I didn't know it was a separate bulb but, the bulb is good. I am getting the right brake light but not the left. No voltage to the terminal with the bulb out. Can this have anything to do with the plug-ins to the master cylinder? The front plug was kinda messed up and I'm not sure I got it plugged in properly...
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Cusser
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Joined: October 02, 2006
Posts: 31378
Location: Hot Arizona
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| Posted: Thu Jul 22, 2021 7:34 am Post subject: Re: Brake lights on 72 SB? |
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| 72VWSB wrote: |
| Can this have anything to do with the plug-ins to the master cylinder? The front plug was kinda messed up and I'm not sure I got it plugged in properly... |
No.
If the right-side brake light works, and the left doesn't, not due to wiring at the master cylinder.
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297 |
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72VWSB
Samba Member
Joined: August 06, 2018
Posts: 707
Location: New Mexico
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| Posted: Thu Jul 22, 2021 7:56 am Post subject: Re: Brake lights on 72 SB? |
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| Cusser wrote: |
| 72VWSB wrote: |
| Can this have anything to do with the plug-ins to the master cylinder? The front plug was kinda messed up and I'm not sure I got it plugged in properly... |
No.
If the right-side brake light works, and the left doesn't, not due to wiring at the master cylinder.
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Thank you! Ok...it appears that there is a wire that crosses over to the right side for the brake light...so, it appears I'm missing voltage at the little terminal block on bottom right of page... You said look for a bad ground...the ground on the inside of the engine compartment looks firm. Is there a way to bypass the ground to test? Course, I get no voltage at light terminal so I think I've lost the power source...
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72VWSB
Samba Member
Joined: August 06, 2018
Posts: 707
Location: New Mexico
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| Posted: Thu Jul 22, 2021 9:26 am Post subject: Re: Brake lights on 72 SB? |
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The tail light works ok, just the brake light doesn't...
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Cusser
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Joined: October 02, 2006
Posts: 31378
Location: Hot Arizona
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| Posted: Thu Jul 22, 2021 4:52 pm Post subject: Re: Brake lights on 72 SB? |
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| 72VWSB wrote: |
| I get no voltage at light terminal so I think I've lost the power source... |
Jam a piece of wood to hold the pedal down, move the seat up to hold the pedal down. Turn on ignition (temporarily disconnect the #15 wires at the coil positive terminal if you're concerned with points burning), check for voltage in that left brake light circuit.
One can always temporarily use a wire with alligator clips at the ends to make a new ground if that's the issue.
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297 |
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72VWSB
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Joined: August 06, 2018
Posts: 707
Location: New Mexico
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| Posted: Thu Jul 22, 2021 5:01 pm Post subject: Re: Brake lights on 72 SB? |
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I checked that Cusser...I'm not getting any voltage to the terminal...but I do get voltage if I turn tail lights on.
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sb001
Samba Member
Joined: May 19, 2011
Posts: 10406
Location: NW Arkansas
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| Posted: Thu Jul 22, 2021 6:18 pm Post subject: Re: Brake lights on 72 SB? |
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| 72VWSB wrote: |
| I checked that Cusser...I'm not getting any voltage to the terminal...but I do get voltage if I turn tail lights on. |
If your right side brake light lights up when you press the brake pedal, but your left side doesn't, BUT you have left side tail light when you operate your headlights (same bulb, two different filaments) then either one of two things:
1. Your BRAKE LIGHT filament is burned out in the bulb, but not the tail light filament (unlikely) To test this, simply swap the known good passenger side bulb over to the drivers side and see if you still have the problem.
2. The SOLID RED WIRE coming off the other side of that left side 4-way terminal connector (the opposite side of where the black red stripe wire that carries power from the brake switches comes in to that terminal) is loose.
The rear light housings use a common ground wire on each side, the ground for the bulbs is through the metal housing, out the single common brown wire on each side, to the ground screw inside the engine compartment. So if you had a bad ground, none of the lights would work.
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I'm the humblest guy on this board.
1969 autostick sedan, family owned since new
1600 SP engine
Solex 30 PICT 3 carburetor
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72VWSB
Samba Member
Joined: August 06, 2018
Posts: 707
Location: New Mexico
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| Posted: Thu Jul 22, 2021 6:52 pm Post subject: Re: Brake lights on 72 SB? |
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| sb001 wrote: |
| 72VWSB wrote: |
| I checked that Cusser...I'm not getting any voltage to the terminal...but I do get voltage if I turn tail lights on. |
If your right side brake light lights up when you press the brake pedal, but your left side doesn't, BUT you have left side tail light when you operate your headlights (same bulb, two different filaments) then either one of two things:
1. Your BRAKE LIGHT filament is burned out in the bulb, but not the tail light filament (unlikely) To test this, simply swap the known good passenger side bulb over to the drivers side and see if you still have the problem.
2. The SOLID RED WIRE coming off the other side of that left side 4-way terminal connector (the opposite side of where the black red stripe wire that carries power from the brake switches comes in to that terminal) is loose.
The rear light housings use a common ground wire on each side, the ground for the bulbs is through the metal housing, out the single common brown wire on each side, to the ground screw inside the engine compartment. So if you had a bad ground, none of the lights would work. |
The bulb is good. Also, I have checked for power at the light terminal...nothing with the brake pedal pressed, right tail light on. I do get power at the terminal when I turn on tail lights... where is the 4 way terminal connector? Inside left engine compartment?
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Cusser
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Joined: October 02, 2006
Posts: 31378
Location: Hot Arizona
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| Posted: Thu Jul 22, 2021 7:23 pm Post subject: Re: Brake lights on 72 SB? |
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| 72VWSB wrote: |
| .. where is the 4 way terminal connector? Inside left engine compartment? |
I believe that it's under the tar board.
Maybe I can check on my 1970 tomorrow when it's light out.
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297 |
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sb001
Samba Member
Joined: May 19, 2011
Posts: 10406
Location: NW Arkansas
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| Posted: Thu Jul 22, 2021 7:57 pm Post subject: Re: Brake lights on 72 SB? |
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| 72VWSB wrote: |
The bulb is good. Also, I have checked for power at the light terminal...nothing with the brake pedal pressed, right tail light on. I do get power at the terminal when I turn on tail lights... where is the 4 way terminal connector? Inside left engine compartment? |
Yes it should be behind the left rear tar board.
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I'm the humblest guy on this board.
1969 autostick sedan, family owned since new
1600 SP engine
Solex 30 PICT 3 carburetor
Bosch 113905205AE autostick distributor |
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72VWSB
Samba Member
Joined: August 06, 2018
Posts: 707
Location: New Mexico
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| Posted: Thu Jul 22, 2021 8:02 pm Post subject: Re: Brake lights on 72 SB? |
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That will be difficult! I just pulled two large hoses through that area for my new A/C unit. And with dual carbs, you can't even get a hand in there!
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sb001
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Location: NW Arkansas
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| Posted: Thu Jul 22, 2021 8:12 pm Post subject: Re: Brake lights on 72 SB? |
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| 72VWSB wrote: |
| That will be difficult! I just pulled two large hoses through that area for my new A/C unit. And with dual carbs, you can't even get a hand in there! |
Or with an autostick vacuum control valve.
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I'm the humblest guy on this board.
1969 autostick sedan, family owned since new
1600 SP engine
Solex 30 PICT 3 carburetor
Bosch 113905205AE autostick distributor |
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Cusser
Samba Member
Joined: October 02, 2006
Posts: 31378
Location: Hot Arizona
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| Posted: Fri Jul 23, 2021 8:03 am Post subject: Re: Brake lights on 72 SB? |
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| 72VWSB wrote: |
| That will be difficult! I just pulled two large hoses through that area for my new A/C unit. And with dual carbs, you can't even get a hand in there! |
That may have been the root cause for your issue !!!
_________________
1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297 |
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ashman40
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Joined: February 16, 2007
Posts: 15985
Location: North Florida, USA
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| Posted: Fri Jul 23, 2021 9:02 pm Post subject: Re: Brake lights on 72 SB? |
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The single black/red wire coming from the master cylinder powers both brake lights. It first junctions at the left side taillight wiring junction and daisy-chains over to the right.
If the right side brake light is working when you press on the brake pedal (ignition switch ON) then power is making it to the rear.
Pull the left side tar paper away from side of the inner fender and find the 8-way junction. ID the black/red wire. Remove it from the junction and clean the connection. Test the wire while you have it out to confirm your get a 12v reading while the brake pedal is pressed.
The rest of your problems sound like a bad ground wire at one or both of your taillights. Remove your plastic taillight cover and use a jumper wire to manually ground the metal case of the taillight to a known good ground and test again.
What normally happens is when the taillight assembly does not have a good path to ground the power attempts to ground any way it can. This means current will flow backwards along non-active circuits like the parking light and brake lights to find a ground. Parking light circuit has a ground at every parking light bulb in the circuit.
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AshMan40
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