Hi I have an old Volvo 740 which has a speed sensor in the differential, I believe it’s a VR sensor as it’s only 2 twisted wires, and a 12 tooth tone ring.
How should I connect the VR sensor to VSS, does the polarity matter, and do I connect the second wire to sensor and, or the chassis gnd.
I would just try and see what happens, but some info says it could be an AC wave from that can damage some ecus?
Some older cars ( old porsche 911) had magnet and Reed relay for speed so verify with multimeter what is resistance between wires. And if is vr polarisation of wiring doesn’t matter for speed input.
1 wire to VSS input, the other to sensor ground. Use shielded wire, ground the shield to chassis ground on 1 end only. in this case polarity does not matter.
It is an AC sine wave but the ECU is designed for it and won’t be damaged.
Once its wired in, select VR sensor on the VSS parameters under sensor type. You’ll need to calibrate vs road speed (either speedo or GPS). This is much easier to do with a second person.