i used 8 magnets, but i think jim is right that there should be 9 (equally spaced.) my speedo was off by about 10%. used the original pickup, just rigged a bracket to hold it close enough to the magnets to pick up the signal.

 

Thanks for all the replies...... Here is the Details of my search......
In 91 the magnetic wheel inside the diff was discontinued making the sensor on the outside of the box obsolete. The later 91 cars used the front left speed sensor pulse going into the abs unit and coming out at pin 16 to the rdk unit and piggy backed it to a FCU frequency control unit, listed in the pet as a speedo control relay at position XIX p.n 964 618 221 00. The abs unit in my car is the same version as the one in the later cars so no change needed there. I am in the process of sourcing a FCU, hopefully from the car i got the autobox from. With this, and four wires (power, earth, sig in, sig out) into one of the spare relay sockets, and i should be back in business. Tried the main dealer for the FCU but they wanted £170.........Wont be going there...... Thanks again for the input...... .........................................JIM

 

That FCU relay is probably just a simple amplifier for the RDK signal from the PSD/ABS controller, course it could also adjust the pulse rate too by some fraction.

There's an interesting note in the WSM under the PSD diagonostics section in Volume III, where they make a note that the pin assignments for the speedo changed from the front left (1991/1992) wheel, to the rear left (1993 and later models).

 

I think that the first thing that I would try would be:
- Epoxy nine equally-spaced button supermagnets to the inside edge of the right rear wheel.
- Mount a bracket to the brake caliper to hold the original sending unit near the magnets.
- Extend the wire harness to hook to the original wires.

Should be cheap - any reason why it wouldn't work?

 

ok guys.......have tried the magnets method and am getting speedo readings now.. Analogue reading is about 50/% of what it should be and digital reding is about 25 % of what it should be.....have not given up though... will vary the gap and change the bracket holding the pick up..might have used a steel bracket....failing that i will try different magnets.. at least i am getting some readings for now...will post some picks of the assembly.......cheers

 

Retain the 50% output signal in a data logger for your ultimate defence in traffic court ....