You can download a service manual, free, at MyMopar. Also the PC board on the cluster as well as the studs/ nuts for the gauges can be a problem. You might want to read through this thread:
Printed circuit pins repair
My 67 had several cluster problems:
1...A bad IVR so I bought an aftermarket solid state one
2...Several of the PC board harness pins were broken or loose
3...The IVR socket contacts were not making reliable contact with the board traces
4...At least one of the gauge studs the nuts were loose/ corroded.
