Re: Brake lite problems

[zm@mhcnet.att.com (Zafer Mehmood [209])]

> 
> Now my brake lights are not working at all.  The ground connections look
> good.  The bulbs are OK.  I suspect that the switch on the brake pedal
> may be faulty.  Just one problem.  I couldn't find a switch on the pedal. :-(
> 
> Duh.
> 
> Oh, I'm dealing with an '89 200TQ.

Bob,

I replaced the brake switch on my 87 5000TQ recently. The location should
be similar on your '89. You have to take out the parcel tray (two screws)
and a duct that runs right in front of the pedals. You should see a long
(about 3") plastic threaded switch in the aluminium frame just in front of
the brake pedal. In fact, there are probably two switches (the other is for
disengaging the cruise I think). The brake pedal switch should have a
connector with two wires. Pull the switch off (needs quite a bit of force).
What look like threads on the switch are really concentric circles to allow
adjustment and a snug fit in the hole. I bought a replacement switch for
about $7 at a local parts place. Installation procedure in Bentley is:
Press down brake pedal. Insert switch into the hole in the frame (there is
a metal clip to keep it snug) until it hits the depressed brake pedal.
Pull brake pedal back to its original (out) position pulling the switch
with it. The switch is now properly adjusted. Plug connector back in and
replace the duct and parcel tray.

Of course, before you replace the brake switch, make sure that is the
problem. You can short the two wires in the connector with a paper clip
to see if the brake lights come on.

> 
> I did find a pair of wires connected to what SHOULD be the brake master 
> cylinder.  They loint slightly upward and forward as they come out of the
> master cylinder(^ that's s'posed to be a "p" above here).  Have I found the 
> wires for the switch.  If I have, how in the name of heaven do I replace a 
> bad switch?  It ain't nuthin' like I expexted to find.  (Maybe I should get
> me a set of Bentleys?)

I think what you have located is the brake boost pressure sensor. This
switch has a brass threaded portion and is screwed into the brake servo
(big round black disk behind the brake master cylinder). This sensor is
responsible for turning on the red brake warning light when it detects low
boost pressure (hey, this is what told you to replace that bad pressure
accumulator!).

Zafer

-----------------------------------------------------------------
Zafer Mehmood				   AT&T Bell Laboratories
zm@mhcnet.att.com			   Murray Hill, NJ