# 6610S NH tachometer bouncing



## jthayes (Apr 12, 2015)

i have an 02 6610S new holland. the tachometer needle bounces and the battery light flashes in synch with the tach. what could be the problem? this model has an electrical tach.


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## sixbales (May 18, 2011)

Howdy jthayes, 

Welcome to the Ford/New Holland tractor forum.

Your tachometer is powered by a winding in the alternator. You have either a defective alternator or a defective battery temperature sensor. Check/clean all of your connections on the alternator to ensure that isn't the problem. 

There is a temperature sensor (thermistor??) installed in a hole in the bottom of the battery tray. If the battery gets too hot during operation, the alternator senses the high temperature and stops charging till the battery cools down. This sensor may be defective. To check this out, go to Radio Shack and get a 200 ohm resistor, and install it in place of the sensor. This resistor causes the alternator to sense "all is well" and start charging. 

Failing that, replace the alternator. Write down where all of the wires go on the alternator (or take a picture) so there's no screw-ups. I found an aftermarket alternator on the internet that did NOT have the tachometer terminal blade on back, so you will have to be careful to get the correct alternator. 

Good Luck. Let us know how it goes.


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## jthayes (Apr 12, 2015)

thanks for the help...john


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