1998 Sportster 1800 speedometer problems

[langhoffs]

I have a new speedometer and also a new speed sensor installed on my 98 Sportster 1800. The speedometer works just fine when bench checked with an external battery, or if the engines of the boat are not running. Once the engines are started and I start moving, the speedometer indicates speed for about 3-5 seconds, then bumps around a bit while heading back toward 0 where it will stay until the engines are restarted. Checked all wires for connection and proper ground. Boat voltage indicates 13.4 volts when engines are running. Can only get the speedometer to work by connecting it to a different battery (not the boats battery). Could there be some type of line noise getting induced into the power going to the speedometer that would cause it to do this? Would a bad charging rectifier(s) cause this type of phenomena?

 

[El Toro 33809]

Welcome to the forum. Sounds like you pretty much checked all the items I would have suggested. Try posting this in the 2-stroke boat section of the forum to see what the folks there think.

 

[Coastiejoe]

I will move your post to the 2-stroke boat forum and leave a 30 day redirect for you.

Welcome aboard,,,

 

[langhoffs]

Thank you very much. Glad to be here. I hope somebody can figure this one out!

 

[Coastiejoe]

Based on your details, it is getting noise/feedback.

I would install a diode in both wires just to make sure it is not getting some sort of a reverse feed.

Other thing you could do is, use a separate battery. It would probably take a month or better for it to discharge.

See if you have any wires that are laying near anything that moves. Wire when activated create a magnetic field around themselves and can feed into others if they are sensitive in nature.