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Tachometer/ Gauge Questions

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I am having trouble with the tachometer and speedometer on my 2003 Sportster.  

When I turn the key to the on position, all needles buzz/zero out except the tach.  Tach does nothing when the engine is running either.  The backlight of the gauge works when I turn on the lights along with the other two gauges.  I have tried to swap the connectors, and the same results, no tach movement.  Would this likely be a dead tach? Is there a way to test the tach itself vs the computer?  The hours on the LCD display also do not change (I've read they dont move unless engine is over a certain RPM)  so could it be there is no signal from the engine to the computer?  


The speedometer is also acting odd.  It is sometimes reading about 50mph when traveling about 15-20, and other times it reads zero while underway.  It is the paddle wheel through the hull by the bilge plug style.  How do I clean that line/ sensor?  I can spin it freely while on the trailer, and the speedometer registers movement as well.  Thinking about upgrading to Precision Star GPS speedometer for this, but I'm including just in case the computer is actually toast and sending bad/no information.


Any leads or recommendations would be greatly appreciated!

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If it doesn't buzz and reset then it's probably the gauge. The guide will tell you to check continuity of the grey wire on the 18 pin connector running to the MDC box under the dash with the grey wire coming from the engine. If you've got continuity there and the grey wire is in the correct place on the connector this it's probably the gauge. There's no practical way to bench test these gauges or the MDC box.

Check this thread if it ends up being the gauge...may still be a couple of Crew Members with a spare.

Edited by drh
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