Brake light issue 87FC35

[Ralph L. Fullenwider]

Hi Alan:

There are several things that can cause this problem, but if we try to
think of them all at this point, I think it would muddy the water to the
point of not finding any thing.

First things to check:
There are 2 break air switches (yes I know you did not use the break, but
that does not make a bad switch good.) that can cause this problem, be it a
boarder line switch going out or one that had become sensitive to a
changing air pressure at certain speeds. These should be located in the
compartment under the drivers seat, out side. Also check any and all
connections in that area.

Then I have seen certain speeds set up a harmonic vibration in tail light
units, and if I remember correctly, you have the elongated Volvo style rear
light sets. The contacts on the lights them selves are fairly close
together and can short easily if not heat shrinked. One way to find this
out is to find a relatively lite used road, and dis connect one tail light
and go to the speed, then the other if no change. And what your looking for
is change when you change the set up from normal.

The over head relay clicking may be due to the spurious voltage being
generated by wiring that is vibrating together else ware. I am going to go
with my gut feeling on it and say that I believe you are going to find a
problem with one of the tail light assemblies or related wiring.

Safe travels,

Ralph and Charolette Fullenwider
"84FC35 "Ruff Diamond"
Duncan, Oklahoma

At 02:13 PM 9/28/2010 +0000, you wrote:
>During a recent trip I noticed my brake lights flickering, then often
>getting stuck on. (I could see them at night in my camera). This coincides
>with a relay in my overhead cabinet chattering.
>
>Here is an experiment I tried. (slowed down w/o stepping on brake):
>1. I am driving at highway speeds, then have to slow down for small town
>2. I flip the switch and turn off cruise (i do NOT step on brake)
>3. As I slow down, somewhere between 35 and 45, a relay in the overhead
>starts chattering. The brake lights (as seen in camera) are now
>flickering, corresponding to relay chattering.
>4. Somewhere below 35, chattering stops, and brake lights are off (as they
>should be).
>5. Now let's say I speed back up, all the time WITHOUT stepping on brake.
>Again, between 35 and 45 chattering starts.
>6. Around 45, the chattering will stop, but OFTEN the BRAKE LIGHTS STAY
>ON. So now, I am driving highway speeds with my brake lights on, and of
>course the cruise will NOT engage. (I used to think I had a cruise problem).
>
>So, here would be my questions:
>1. First, does this chattering at certain speeds and then staying on make
>sense to anyone?
>2. Where is the brake switch? (I have tried pulling up on pedal)
>3. Electrically, what is SUPPOSED to happen when I step on the brakes.
>(and where would this overhead relay fit into what happens)
>
>On the good news, just got back from a GREAT 10 days in Durango and
>Silverton Colorado. Weather was fantastic, leaves were turning, and had a
>good time Jeeping on the mountain 4x4 trails.
>
>Thank you,
>Alan Johnson
>87FC35
>
>
>