Temperature gauge not working.

[HypnoToad]

I notice last week the temperature gauge was a bit dodgy by Friday it had stop working.
On Saturday I grounded the green wire from the sending unit and the gauge moved to top.
The manual said that the sending unit was broken and needed to be replaced.
Replaced it on Sunday with a second hand sending unit and it worked for about a day and has stopped again.
Do I need a third sending unit or is something else gone?
Thanks

[HypnoToad]

Testing the sender

Well I have done the ohms test described in the manual and was getting some odd readings from both sending units.
Some one must have had this problem before am I on the right track?

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[Hordpower]

I know I sound like a broken record at times, but whenever tach/temp gauge issues crop up it is 90% likely the wire harness ground. There is a green wire with ring terminal that connects to the brake reservoir bolt under the seat. Clean that connection up, and most of the time it cures things. Sounds goofy I know, but try it. Also check battery cable connections.

[motorcycleman]

I second hords response.... when things electrical seem strange, such as the turn signals causing the headlight to dim, or both sides come on at once, it is indicative of a bad ground.

[HypnoToad]

Also the colder the air temp is the long it take before the front head light comes on. maybe up to 5 seconds after I hit the switch.

I'll have a good look at the green wire under the seat and give it a good clean