Rumble bee tachometer problem

[fabiolo]

Hi guys,
I have a 2004 rumble bee with a tachometer problem
Just turned on everything works fine but after a few minutes it works randomly.
Does anyone know what it would be like to give him this problem?
Do you know where the signal comes from? Does the signal come from a ignition coil or somewhere else?
Thanks for the replies and sorry for my English

 

[HemiLonestar]

Tach is part of the cluster, which is an integrated computer module unto itself. If you tach is messed up, you'll have to replace the whole cluster.