Auto-Check Brake Light problem

[Al Powell]

Friends, I need some help diagnosing a problem with my 1990 200 with 
134K miles.

The problem: the auto-check system's alert indicating brake problems 
(O) comes on after driving a few feet every time I use the car.

I know this is not a trouble alert from the front brake pads, because 
the first thing I did was to visually inspect the pads, determine 
they were safe to drive, then cut their sensor wires (on the pad 
side, not the car's wiring harness side), then twisted the brake pad 
wires and soldered them together on the piece which plugs into the 
car's wiring harness.  The auto check therefore cannot be detecting a 
problem with the pads...because the circuit is complete on both 
sides.

But that didn't make the alert go away!  I've checked the Bentley up, 
down and sideways - and I can't really figure out what CAN be causing 
the signal, because it appears that the front brake pads are the only 
things which can send a signal to that auto check circuit. However, 
here's what I have figured out:

- The (O) alert never comes on unless the car is moving. If I leave 
it stationary and idling (in Park or Neutral) and pump the brakes and 
use the parking brake, I cannot cause an alert to show regardless of 
how long I wait.
- If I have the car moving - even drifting in Neutral without using 
the brakes at all - and turn the key on, the alert (O) will show 
within 40-50 feet of travel.
- Turning the ABS system off manually does not prevent the alert from 
occurring.

After finding the above, I thought maybe I was getting a trouble 
alert from the ABS system - although according to the Bentley's 
wiring diagram, I can't see that it is connected to the auto-check 
system at all. Seems like its' alert is the light below the 
auto-check window.  But ABS sensors seem like the only things that 
would respond to car motion and not to use of the brakes. Then again, 
why would it do that when the ABS system is turned off?

I disconnected the connections for each front brake ABS sensor at 
their locations near the tops of the shock towers.  The Bentley shows 
a test for the sensors - use an Ohmmeter across the contacts on the 
female side of the connector, and resistance should be between 0.8K 
and 1.8K ohms. On both front sensors, I am unable to get any 
resistance reading at all - it shows as an open circuit. But I don't 
really know whether I should worry about that or not. Seems like the 
chances that both front sensors would go bad at once are negligible. 
 Maybe the readings are due to old sensors (or a Bentley mis-print)?

I need to take this car on a 2200 mile trip in two weeks.  I know 
there is no real safety issue, so I can easily drive it with the (O) 
warning showing, but it's a PITA.

I welcome ideas and suggestions, especially if there's someone who's 
BTDT.

Since I'm having trouble keeping up with digests, replies directly to 
me at powellae at home.com would be much appreciated.  TIA, friends.
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Al Powell
Fort Collins, CO
powellae at home.com
cougfan1 at gocougs.wsu.edu
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