1993 K75S (ABS) Speedo/Tach Gremlin

[GordonOlson]

HELP! Within the last week the speedometer and tachometer on my 1993 K75S seem to have become possessed. With no pattern (at least no easily discernible one), the speedo and tach do the following: go dead; hold at a given number despite changes in engine/bike speed; work perfectly fine; appear to be inaccurate (i.e., engine speed and bike speed do not appear to be in sync). All other instrument cluster functions (ABS light, neutral light, high beam indicator, gear indicator, oil and battery warning lights, turn signal indicators, etc.) always perform normally.

After having a small heart attack when I checked on the price of a new instrument cluster, I am wondering if anyone out there has any idea what might be going on.

Also.....I am (was?) planning to go to the RA Rally next week and am curious whether there is a potential problem with a 2-3,000 mile trip when the speedo and tach are acting up. Obviously, I recognize that if they both go out I will not have precise data on engine/bike speed. I presume that the odometer would also quit were the speedo to pack it in. I will be traveling with a buddy so I will know how far between fill ups and I think that I can judge engine/bike speed. Do I risk losing all the other instrument cluster functions?? If so, I think I may have to sit this trip out until I get the problem(s) sorted out.

Any ideas/suggestions welcomed.

Cheers,
Gordy

 

[roncooper]

I have an idea about the speedo. Ride the bike and see if the turn signals self cancel. If they do, then the sensor on the final drive and connection near the rear brake reservoir are good. The next step in this case would be to pull the cluster and check connections there. Both times my speedo lagged or quit working, the connection at the brake res. was the problem.

Someone else may have an idea on the tach. I think the tach being erratic can be a sign of a pending ignition failure.

 

[GordonOlson]

Ron: I just checked and the self-cancel feature on my turn signals is NOT/NOT working. It always used to work fine. What's my next step?
Thanks for the help. Gordy

 

[98lee]

There is a plug in the speed sensor wire. The speed sensor is the black item on top of the final drive with the wire running forward along the swing arm. you also have the ABS sensor wire running alongside of this wire. The plug is wire tied to the frame tube just forward of the coolant overflow bottle. It's one of the smaller two wire connectors. Check it for solid connection.

A way of testing the speed sensor is remove the sensor (1 retaining bolt), then gently wiggle and pry up (there's an o-ring holding it in).

Turn key and kill switch on, hold a soldering iron or gun NEAR the tip of the sensor. Speedo should register somewhere between 20-40mph. I forget the number, but it's not important. Then try wiggling the wires near the plug or near the sensor. If the speedo needle jumps up and down, the wires in the sensor or the harness side of the connector are bad and you need to repair or replace it.

 

[98lee]

Also, just for giggles, check the voltage at the fuses (through the hole in the top of the fuse-to ground) fuses in, key and kill switch on. Should all be battery voltage with the possible exception of #2 (might be 1v low).

Get back with results.

 

[Crazychester]

1988 K100 RS/SE Elec. prob. HELP!!!

Don't mean to hijack this thread but I developed a similar problem on my 1988 K100 RS/SE. While driving down the road, speedo and tach went dead and later found out my brake light no longer worked. Everything else on the gauge cluster seemed to work. When I got to my destination and shut off the ignition, the bike failed to start. The top fuse on the panel was blown. After replacing the fuse, I attempted to start the bike only to find that it blew the new fuse. After many hours of diagnostic by my trusty local BMW wrench (and hundreds of dollars in labor - ouch!), an apparent short was discovered, the offending wires repaired, but the problem remains and is elusive. Any ideas anyone?