'91 Jetta cruise control question

Have a diesel with cruise that has not been working, so did the
diagnosis procedure listed in the Bentley manual. The procedure is
fairly simple, using a jumper wire and indicator light. The cruise
control/turn signal switch handle and and vacuum pump work fine. When
checking the functioning of the small indicators that mount on the
clutch and brake pedals, the power seems to be backwards. If I read
the manual correctly, I connect a lead, with the indicator light,
between the #1 and #3 positions on the cruise control's brain. With
the key ON and the cruise ON, when I step on the brake or clutch, the
light is supposed to turn on. My problem is that the light is ON when
I first hook up to the #1 and #3 positions, and goes OUT when I step
on either of the pedals. Have I somehow made some power connections
backwards? Thanks for any help you folks may provide.

jettaman8691 wrote:
 >
 > If I read
 > the manual correctly, I connect a lead, with the indicator light,
 > between the #1 and #3 positions on the cruise control's brain. With
 > the key ON and the cruise ON, when I step on the brake or clutch, the
 > light is supposed to turn on. My problem is that the light is ON when
 > I first hook up to the #1 and #3 positions, and goes OUT when I step
 > on either of the pedals.

What you see is normal. When not touching either pedal, there should be
continuity from terminal 3 to ground. Thus a test light between terminal
3 and terminal 1 (positive supply) should light up with no pedals
pressed and turn off when touching either pedal.

On some A2 cars, terminal 3 was connected to the brake switch, the other
side of the brake switch was connected to the clutch switch, and finally
the other side of the clutch switch was connected to ground. On others
the clutch switch was connected to the brake lights switch instead of
ground. In this configuration the ground circuit is completed through
the brake light filaments (thus if all brake light bulbs were out the
cruise wouldn't work). I don't think this is relevant for your problem,
I mention it because it could potentially cause confusion when
troubleshooting.

The next test to do (not sure if it is mentioned in Bentley or not) is
to hook a voltmeter (don't use a test light) between terminal 5 (speed
sensor) and ground (e.g. from terminal at the harness that plugs in
to the brain. Then drive really slowly across a parking lot (sloooow
walking pace only). It doesn't matter if the cruise main switch is on or
off and it doesn't matter if the brain is plugged in or not. The voltage
should alternate between around 0 volts and some higher voltage (5 volts
or 10 volts, I can't remember). If the voltage is not alternating, the
speed sensor is probably bad. It is mounted to the back of the
speedometer in the instrument cluster. Small Hall-effect sender in a
plastic holder, mounted with two screws. The flex circuit from the
instrument cluster connects to it. I believe there were two different
kinds in use depending on whether the car has the MFA or not.

Both the speed sensor and the cruise brain are pretty easy to find at
the junk yard. The VW part number is printed on the housing, and the
unit was used in a wide variety of both Audis and VW's for years and
years. I picked up a *complete* cruise control system for my '87 for
under $50 at a local junk yard.<!-- ~MESSAGE_AFTER~ -->