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Thread: Erratic bouncing tach needle issue sovled

  1. #1
    A few weeks ago I noticed my tach needle "twitching" a bit, mostly right around 2800 rpm. It got worse over the next week until it was going completely spastic. After reading a bit, I figured I had a harness problem around the steering head, so I pulled apart the cowl and untaped the harness back into the plastic guide on the frame ('06 XB12Ss). I thought I might have found a bad splice, so I repaired it and put it all back together. It seemed good for a day or so, but the twitch came back.

    Since the tach wiring is pretty simple with one wire straight from the VCM to the instrument cluster, I figured that either the wire had a problem deeper in the harness or it was an ECM or cluster problem. I have a lot of experience in the automotive industry with wiring harnesses and connectors, and while the ECM connectors are well sealed and robust, the connector at the cluster is not, regardless of the little rubber "bootie" installed over it.

    I started with the easiest possible fix - Dow Corning #4 Electrical Insulating Compound. I lightly filled the harness connector sockets and reconnected it to the cluster. I've ridden several hundred miles since and I have yet to catch the tach doing it's little jig. Thankfully it was that easy - keeping my fingers crossed that it stays fixed!:D

    Chris

  2. #2

    Lightbulb Chasing the problem at the wrong end of the harness!

    10 years later I finally fixed the real root cause of this!

    Originally, it appeared to be fixed by applying some Dow Corning dielectric grease to the connector at the cluster. I went after the harness at the steering head on a wild goose chase - it was fine. The problem would go away for a while, sometimes even several years, before it would come back. Finally it became much worse and fooling with the connector and grease didn't help. Finally, while out riding I decided to pull over, pop the seat and simply unplug and reconnect the ECM plugs and check the grounds, relays, fuses, etc. I got going again and the problem was gone! OK, so that at least gave me a good clue.

    I started searching for info again, and came across mattyMaxMac's post on another thread mentioning the ECM solder joints and thought AHA!!! I wasted little time performing a cover-ectomy on the ECM, indeed finding some suspect solder joints under magnification, and re-soldering the connections. I let the Loctite non-corrosive clear RTV sealant cure 24 hrs. and was stoked to test it out. I fired it up and all was good....until I sat on the seat. As soon as I sat down the tach started it's seizure, but if I stood up, it stopped. I did this three times, same results. ??????!!!!!!????? WTF? (and no, I'm not that fat, just a wee bit fluffy). I've been soldering for 35+ years so I was pretty confident my repair work was OK and needed to look at the rest of the stuff under the seat.

    First I went about cleaning and tightening the grounds. I was just about to reconnect the harness to the ECM when something caught my eye. It was a tiny spot on the underside of the bundle. I looked closer and saw shiny copper and pink wire insulation. DOH! The tach wire! I looked down in the frame and saw a similar bare copper spot on one of the ground wires that ran perpendicular under the harness Actually, it was several bare spots at different locations, all very small.

    I'm pretty sure this has been the cause all along. Any time I'd futz under the seat (new battery, charging battery, checking wiring, etc.) I'd move the harness just enough so it would not ground out the tach. After a while it would either move back into it's old position or wear a new spot, which might have taken years. Eventually it would cause the tach to start freaking out again. I re-routed the ground and fixed up the harness and permanently solved the issue.

    As a side benefit, the bike does seem to run a little better since the ECM rework, although I had no issue with it prior. She's been a reliable machine for 27K miles so far.

    Chris

  3. #3
    Senior Member Mesozoic's Avatar
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    I have a cluster harness issue where turning the bars side to side causes the trip odometer and other parts of the cluster to reset. I've been living with it for a while now, but I did isolate it to the section of harness that runs up along the front of the frame (near the steering head). The power wire, specifically, loses power turning side to side. I forget exactly how I isolated it, but the issue was not with the connector to the cluster, but somewhere below it - might be a fatigued section of harness and I'll probably need to replace entire sections with higher quality wire when I finally get off my arse and deal with it.

  4. #4
    Senior Member Mesozoic's Avatar
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    Quote Originally Posted by Barrett View Post
    The dreaded and highly documented "Red + main feed wire" issue.
    That's great, Barrett! I would love to read about it - do you have any links to threads RE resolving the problem? I searched, but didn't find anything conclusive.

  5. #5
    Senior Member Mesozoic's Avatar
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    Quote Originally Posted by Barrett View Post
    The dreaded and highly documented "Red + main feed wire" issue.
    That's great, Barrett! I would love to read about it - do you have any links to threads RE resolving the problem? I searched, but didn't find anything conclusive.

  6. #6
    Senior Member Barrett's Avatar
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    Links? Will personal experience and expertise suffice?
    On many of the assorted Lightning and X/XT models, there is what I refer to as an assembly flaw combined with an ill-conceived wiring design....and it resides in the main loom at the steering neck area. A combination of several factory splices along with both throttle cables located in precisely the same area, spells eventual trouble for many of these models.
    Symptoms: occasional flashing or erratic behavior of 1 or more of the CEL...neutral light...oil pressure light....low fuel value light....random sweeps by both gauge needles....blown ignition fuse.

    Very tedious solution in that the obvious repair is unraveling of the main harness at the steering neck...close examination/inspection...repair of offending wires and harness area as required.

    XB neck harness.jpg

  7. #7
    Senior Member Mesozoic's Avatar
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    Personal experience suffices, for sure! It sounds like I've got exactly the same problem - I feel that I will simply need to rebuild that section of harness, eventually.



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