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Hi all

I have been having an intermittent issue with the speedo on my 75 TS. When it works it works fine. Then, randomly, it will wind all the way round past 250km/h and stay there until i either switch the engine off or press the trip meter reset button.

My car has the black jaeger box under the rear seats and i have tried replacing it with another but to no avail. I am assuming if the sender had failed it would just fail dead. So most likely it is in the speedo head unit.

Has any one opened one up before? Any idea what part of it could cause the symptom I am getting?

Thanks
 

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Almost certainly the head unit. The box sends out a pulse train. I cannot imagine a fault that would make it run wild.
 

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I've had this on my previous car. I tried swapping out the gearbox sender (nope), underseat amplifier (nope) then finally the whole dash pod (I had a spare car at the time). That did it.

No idea why they do this, the current car did it too while the previous owner had it but this time the symptoms included lots of exciting smoke in the cabin! He swapped the dash pod and it's (touch wood) worked perfectly for the 90,000 miles it's done since.
 
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