On going issue with tach

[Phil57]

I need some help. My tach has not worked right sense I bought my bike this past February. It works for the first four or five miles but not accurately. After that it stops and will not register until I turn off the key and restart the bike. I tried a new tach and I get the same thing. The tach does not seem to be accurate at low rpm but seems to work at high rpm until it stops completely. I also noticed that it will jump with the turn signal or flash of the bright lights. I have put around 4ooo miles this year and the bike always starts and runs great. The bike is all stock except for Cobra pipes. No extra lights or other electric add on. I have checked and cleaned all of the connections that I can find and checked the battery terminals as well as the ground at the frame. I do not have a multi meter to check further. Could this be a bad battery or alternator?
Thanks

[Ferris Leets]

Sounds to me like the pickup wire for the Tach is either loose, corroded or the wire is broken but still making some contact.  You should get a multimeter so that you can check for continuity.  If you have a good wiring diagram you can follow that wire all the way from the sensor to the ground on the other side of the Tach.

[Ricky-D]

"I also noticed that it will jump with the turn signal or flash of the bright lights. "

To me,,,,,, This would make me think that you have lost a ground somewhere.

***

[Phil57]

I thought ground also and the search points to that also. What would lose ground after tuning for 4 minutes.

[Ricky-D]

I thought ground also and the search points to that also. What would lose ground after tuning for 4 minutes.

Although that is one way to look at the problem I take an alternative view (such as) where current is flowing thru a different path to reach a ground. Sometimes, but not necessarily, (as an example),,, you might lose a dedicated ground in an instrument, but by way of a ground in a different instrument ground is regained but is now routed thru that secondary instrument by way of a common connection such as the ICM or a temperature sensor.

The end result being the one instrument is wholly dependent upon the secondary instrument and it's operation parameters.

***

[R J]

Many moons ago, we had a I/State in the shop and the ground was lost in rubber boot under the right side cover.   Same problem you are describing.

Have you been doing any playing around in the electrics.    By that I mean added an electrical option.    Trailer wires, driving lights and etc.    If so, look there 1st.     You are looking for a bad connection on a GREEN wire............

Good luck, chasing ground wires can be a pain in the rear side.

[shortleg]

  You might look at the connection at the ICU
for good contact.
         Shortleg[Dave]

[RP#62]

Some things to consider:  The tach needs three things to operate: power, a ground and a tach signal from the ICM.  The wire that provides power to the tach also powers the indicator LEDs at the bottom of the tach (coolant, oil pressure and sidestand warning).  When it quits working, stop and put the sidestand down and see if the light comes on. The wire that provides the ground also provides a ground to the background lights.  When the tach goes screwy do the background lights follow suite?  If there's no problem with either of those, it must be the wire that provides the tach signal.  There is a single bullet connector on the tach signal wire in the headlight shell (its on the yellow wire with the green trace). Pull it apart, make sure its clean and was securely connected. The only thing left is the connector at the ICM, check to make sure there's no corrosion.  Let us know what you find.
-RP

[Phil57]

Thanks for all the input so far. This is what I did today. I repaired bare wires under the rear fender. Three were bare but not the ground. Checked the icm conection looks good. The tach wire in the headlight is good. The tach is new. I am still trying to figure out the multiple meter that I bought Friday. How would I check the voltage from the icm to the tach with the meter. The manual says the voltage should be 10.5. Can I check this with the meter. It says to check it with a peak voltage meter. 
Thanks for the patience I'm learning as I go and really appreciate the help.