The brake pad system on your car has sixteen external connectors in the
circuit. If any
one of those connectors has poor or no contact, the system sets the brake pad warning
First, you need to be familiar with the plug set-up on the bottom of the Central Electric
Panel, which varies in different year models.
On your '83, there are 25 plugs, identified from A to Z, with I not used. The plugs are
arranged from A on the left end and X on the right end. The two short plugs in the center
are Y and Z.
All except for Y and Z have eight available terminals per plug, arranged:
Thus, when you see a code B5 on the wiring diagram, it means the connection in the lowest
right-hand side of the second plug from the left. C3 would be the third connection up the
left side of the third plug from the left.
Plugs Y and Z are the same idea, but located in the center with only six connections,
(Note for owners of later models - your coding and arrangement are different.)
OK, down to business.
The circuit starts with a brown/black wire in Terminal 19SW on the Central Warning Unit.
SW means swartz, or black. Half the connectors are black, half are yellow (GE). This is
the terminal identified as #19 on the black side.
So, starting at Terminal 19SW, the brown/black wire runs to D8 (top right terminal on the
4th plug from the left).
Behind the panel (more connections!), the circuit runs to U5, where a brown/black wire
runs to a connector on the left rear pad sensor.
From the left rear sensor, a black/brown wire runs to the right rear sensor.
From the right rear sensor, a black/brown wire runs to U8.
From U8, the circuit runs to Q8 behind the panel.
From Q8, a brown/black wire runs to the right front sensor.
From the right front sensor, a brown/black wire runs to Q7.
From Q7, the circuit runs behind the panel to K6.
From K6, a black/brown wire runs to the left front sensor.
From the left front sensor, a black/brown wire runs to Terminal 20SW on the Central
Warning Unit, completing the circuit.
All of this is shown clearly (once you understand the plug coding) on pages 97-169 and
97-175 of the wiring diagrams found in the Factory Workshop Manuals.
If you have not done so, I would strongly urge you to buy the complete CD set of 928 tech
info prepared by Jim Morehouse. There is a HUGE amount of info in the set, including the
manuals, tech spec booklets, changes by year, etc., etc. Arguably the most important
purchase you can make for your 928. Jim's email is jim928ATptd.net - change the AT to @.
While this seems complex, it is actually a simple circuit.
If I were going to find the problem, I would first put a temporary jumper between 19Sw
and 20SW on the Central Warning Unit, which is under the "dead pedal" under the driver's
If the warning goes away, the problem is in the circuit somewhere. If it doesn't go away,
the problem is a faulty Central Warning Unit.
At that point, I would get a multimeter or Ohmmeter and a ten- to twenty-foot piece of
wire - whatever is handy/cheap.
Remove the jumper. Hook one end to the wire that connects to 19SW. Then, go to each
sensor in turn, in the order given above. Check for continuity (zero to less than five
Ohms) between the long wire and either of the black/brown wires at the sensor connector.
If you have continuity on either of the brown/black wires, the circuit is good to that
Plug that sensor back in, go to the next one in the sequence.
When you find the connection where you have no continuity between the long wire
(connected to the start of the circuit at 19SW) and either of the brown/black wires, the
problem is either in the brown/black wire back to the last sensor you checked, or the
connections at that sensor, or that sensor.
Hope that this helps!