Twisted pair wiring

Discussion in 'Automotive Electronics' started by shortbus, Mar 13, 2019.

  1. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
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    Does anyone know if the wires from an ABS speed sensor actually needs to be a twisted pair? The OEM doesn't that way but the aftermarket harnesses don't seem to be doing it like that. It is a low voltage AC signal from the sensor, that varies with speed. I think they originally were a square wave DC signal when ABS first came out but have changed now to the AC output.

    The reason I'm asking is the car is old and don't want to spend a lot of money, the twisted pair is ~$100, and a straight pair wire is $10 for the same harness.

    @bwilliams60 could you chime in on this please?
     
  2. bwilliams60

    Senior Member

    Nov 18, 2012
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    Hi shortbus. It is recommended that all ABS sensor wiring be of the twisted pair variety on most vehicles I have ever seen. The reason is that any communication wiring or wiring sending signals, need to be twisted to reduce noise(reflections and echo) in the system. A corrupted signal is very possible with straight wiring. The insulation on twisted pairs is supposed to be unique in comparison to regular wiring, as it tends to form a capacitor to shield itself from noise. If you want to try this on the cheap, you can try and take two normal wires and stick the ends in a drill and the other end in a vice. Spin the drill until you get about three turns per inch. Add your connectors on and try it out. I have done this in a pinch but not a recommended repair.
    You can put an oscilloscope on it and see if there is any noise. Hopefully not.
    what is wrong with yours that you are replacing it?
     
  3. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
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    Hi bw, the car was sold because the guy didn't want to replace the wheel bearing, left front, he was told that was the problem, the tone ring and pickup are internal to the wheel bearing (04 Impala). Other than that the car is in great shape. I measured the resistance on the speed/abs sensor and it was pretty much the same as the right side that's not throwing a code. So then I checked continuity on the wires from the sensor, and both are open. The internet is full of GM cars from that era with the same problem and always seems to be the driver side for some reason.

    Why would an AC signal have a problem with echo? I can see something that is making a count but this is strictly a voltage level signal. This wiring was made at the time GM Packard Electric started sending a lot of small harness work like this to Mississippi. I actually worked where this harness was made before sending it there, Warren, Oh. Actually worked on the twisting machines too. The twisted pair wire was made from regular straight wire that the rest of a harness used, only twisted, nothing special about the wire.

    Twisting it myself was what I was thinking if it needs to be a twisted pair.
     
  4. bwilliams60

    Senior Member

    Nov 18, 2012
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    With regards to echo, reflection, I was talking in general about the need for twisted pair. Most of the work I do with twisted pair is CAN Bus work and it is imperative that it is twisted for that reason. The insulation on CAN Bus wiring is also supposed to be different from normal wiring. Sorry for the confusion.
    As for ABS wiring, it may be just normal wiring that is twisted. Like I said, I know I have done the drill trick on ABS before with no ramifications.
    I am concerned about two wires being open though. Something doesn't sound right. I am not sure which style of ABS your vehicle has but we can figure it out pretty quick. Is there voltage going to either of those wires at the sensor with the key on? My other question is about the wheel bearing. Was the entire hub changed or just the bearing?
     
  5. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
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    Hi again. The bearing doesn't need changed, that is what another mechanic told him because of the code that was read. The hub, bearings and sensor are all in one. All of this was before I bought the car. It seems like for some reason water gets into the wires and they break, or that's the reason all of the "experts" give. You can actually pull on the wires and they will break, or at least that's what they show on a couple of Youtube videos. And one of them is even from Standard Ignition showing how to do the checking. I don't have a ABS code reader, yet, should be here Saturday so I can see the code myself. But like I said the sensor has continuity and the same general resistance on both sides.

    But from when I worked on the twisting machines, if the free end of the twister didn't move easy enough it would break strands in the wires. The twister was like a lathe bed, one end was fixed, like a head stock and did the spinning of the wires., the other,tail stock end had to be free to move on the bed of the machine but keep the wires still. When the head stock stopped turning the wire would relax and the tail stock would be free to return part way until the wire was taken from the machine. The wire was actually over twisted to get the correct twist per inch when relaxed.
     
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