Date: Mon, 26 Dec 2005 09:43:25 -0800
Reply-To: mark drillock <drillock@EARTHLINK.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: mark drillock <drillock@EARTHLINK.NET>
Subject: Re: Finding and Accessing the Brake Light Switch
In-Reply-To: <11dcddf80512260838l5b57f6b4l8b34f1f8288f8e97@mail.gmail.com>
Content-Type: text/plain; charset=us-ascii; format=flowed
OK, it sounds like you have more than one problem with the brake lights.
One or both problems may be intermittent as well.Use the straight pin
method and measure only voltage when checking the power to lights.
Continuity checking leads you down false paths, as is clear by your
post. Most people don't have any idea what is reasonable for various
continuity readings so they can't evaluate the results.
You should leave the bulbs IN for voltage measurements. As TJ has
pointed out, you can have voltage looking good with no bulbs but
dropping to nothing when the bulb is trying to draw current. Corrosion
at a connection is the likely cause if this occurs.
1. When you are checking for voltage at the rear sockets, where are you
putting the minus lead of your meter? Make sure it is real chassis
ground, not a brown wire. After you check for proper voltage that way,
check again using the socket ground to see if the voltage is still fully
good. Bad or weak grounds are very common in all areas of our 20 year
old vans.
2. What VOLTAGE is coming out of the front brake switches? Unplug each
in turn and measure the voltage on the wires of the other with the brake
pedal pushed. Put the minus meter lead on chassis ground.
3. What VOLTAGE is present in the black/red wire on BOTH sides of the
round 7 pin connector with the brake pedal pushed hard or one of the
switch connectors jumpered? Put the minus meter lead on chassis ground.
Mark
Christopher Gronski wrote:
>OK, when testing continuity (ie: not volts) on the switches the one
>towards the driver seems to be functioning, it does not drop quite to
>zero with the pedal but very close (0.23 to 0.13). The second switch
>further away from the driver is not showing continuity (ie: I am
>gettin 1 all the time)
>
>When I bridge the connector manually (ie: its off the switch and I'm
>using a copper wire with flattened ends bridging the switch) the brake
>lights come on without touching the petal (as expected). Both lights
>worked briefly but then only the passenger side bulb worked.
>
>If I take out the brake bulb I get 12v to the socket with the brake
>pedal pushed and 0v with it not pressed (as expected). But If I put
>the bulb IN THE SOCKET I do not get brake lights, the bulb looks fine
>and was tested for continuity and is working. IT IS NOT THE BULB the
>bulb itself was working when I manually bridged the switch. Morover,
>WITH THE BULB IN, if I measure further back on the wire I am all of a
>voltage is all of sudden back to 0.5v on the brake wired (pedal down).
>
>So I get 12v at the brake bulb sockets as long as there is no bulb in,
>but my voltage drops to 0.5v as soon as I put a bulb in.
>
>The other weird thing is if I measure continuity between the brake
>wire and any other taillamp wire (signals, hazzards, reverse,
>whatever). I get continuity.
>
>I am driving myself crazy, what is this?
>
>Chris
>
>P.S. I cut out ALL the trailer wiring.
>
>On 12/25/05, mark drillock <drillock@earthlink.net> wrote:
>
>
>>Where exactly are you putting each of the meter probes?
>>Does it drop to zero volts when the pedal is released?
>>
>>The brake switches are doubled up for safety. It is unlikely they would
>>both be bad. The problem is far more likely to be in the left taillight
>>area or the engine compartment wiring junction box. There are 2 round 7
>>pin connectors in the box. One of these has all the wires for the rear
>>lights. The brakelight wire is black/red stripe.
>>
>>Using a straight pin, push the pin into the wire. Push through the
>>insulation and aim for the center where the metal is. Measure the
>>voltage on the pin while someone pushes the brake pedal down hard. Put
>>one probe on the pin and the other probe on bare metal ground in the
>>engine compartment. On the same round connector are 2 wires that are
>>grey with a stripe. These should have 12 volts when the headlight switch
>>is on. Push the pin into one of these to verify your test setup. If you
>>can't find 12 volts on one of these then you are doing something wrong
>>and not finding 12 volts on the brake wire won't mean much.
>>
>>Mark
>>
>>Christopher Gronski wrote:
>>
>>
>>
>>>Right now I'm only getting 1 volt at the brake lights with the pedal depressed.
>>>
>>>Chris
>>>
>>>
>>>
>>>
>>
>>
>>
>
>
>
>
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