Tachometer stuck at 2500

[AXEL]

It was working fine all day and then I noticed it's stuck at 2500, even with the engine off. I tried tapping on the gauge, not helping. At one point I shut the engine down and it did go to zero and worked a bit, but then retuned to 2500 on or off. I haven't started to trouble shot yet, I'll get to that this weekend. Just wondering if anyone had any ideas? The engine is a Universal 25 XPB.

 

[Stu Jackson]

It's connected to your alternator. Check the wiring at the back of the alternator. What color is the wire? Look here at the wiring diagram:
http://c34.org/wikiwp/?rdp_we_resource=http://c34.org/wiki/index.php?title=Engine_Harness_Upgrade

 

[Bill Roosa]

yea, it is getting a signal from some where it is not supposed to. Think some source of AC voltage other than the alternator/sensor unit. The tach reads an alternating current's frequency so the voltage is not that important. Battery chargers and inverters are good examples. they have "ripple" in their outputs and can also cause "ripple" in their power supplies. Try shutting down those devices (and other electronic stuff like AP, plotters etc.) to see if it effects the tach.
good luck