JBasham
JBasham HalfDork
5/16/18 8:26 a.m.

I need to replace the wiring harness that runs to the ABS rear wheel speed sensors in my E36.

The stock wire is unlike anything I've seen in a BMW wiring harness.  The voltage conductor is insulated pretty thickly with something like PVC, and then the ground conductor is wrapped around that insulation at a very low rate of twist, like just a few wraps per inch, and another PVC-ish layer sheathes that as the pair.  And it's not bundled in with any of the harnesses that run to the trunk.  Just the two leads by themselves, taking a completely different route to the dash.

I think I understand why each sensor has its own ground lead.  Because the signal is magnetically induced, it doesn't have that much voltage, and ground loops might wash it out.  Right?

Is there any reason I can't replace it with twisted pair 22 AWG solid copper wire with Teflon insulation?  My logic is, that stuff is the backbone for CAT 5, so it must be pretty good at small signals without getting noised up.

irish44j
irish44j UltimaDork
9/6/18 3:51 p.m.

well, some spammer copied your thread and reposted it. Oddly enough, people actually replied to teh copycat thread. Here's what they replied, haha. Figured I'd repost it into your actual thread, in case you hadn't figured it out yet.

Knurled.
Knurled. MegaDork
9/6/18 7:09 p.m.

Yeah, really odd wasn't it?

 

In response to the OP, it is shielded not to protect the car from the sensor, but to protect the sensor from the car.  Automobiles are extremely noisy things in the EMF sense.  Power flying this way and that and spikes everywhere from solenoids and relays opening and closing.

Donebrokeit
Donebrokeit SuperDork
9/6/18 8:00 p.m.

The shielding (twisted wire and wrapped grounded cover) helps to keep the signal sharp and helps protect the ABS/ CAB unit. I have seen a few units damaged due to a lack of shielding.

 

Paul.

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