Hi,

That is strange behavior indeed. I haven't seen it happen, although my experience is limited to those electronic speedos before ABS, which brings some subtle differences to the gauge circuitry and not so subtle changes to the tone ring and sender.

In your case, I would be curious about how this came about. When in its life did you notice this? An easy explanation would place some errant iron filings or other ferrous debris inside the gauge's D'Arsonval meter movement, causing the needle's motion mechanical interference. Usually this only occurs after a bit of tinkering in the area.

If this just came about without provocation, perhaps, as others may have experience, the circuit's decoupling capacitor may be drying up with age, allowing undesired signal from alternator or ignition to be coupled to the sensor input on the speed counter chip. I think there's a suggestion in the 700/900 FAQ list to replace the capacitor, though for differing symptoms.
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Art Benstein near Baltimore

When you've seen one shopping center you've seen a mall.