Probably not wire harness if its all of them. IVR or connection to IVR (fuel gage) will effect the Fuel, Temp and Oil Pressure. Poor connection on the board or weakenss will be just Temp & Oil pressure. That was the only real issue on my board.
Try to do some diagnostic before he comes. IVR surgery will be a different project.
The 1966 Master Tech filmstrip and movie cover the gages real well, and pretty easy to understand.
Some links here:
Rallye Instrument cluster voltage limiter - 68 Barracuda
If you do have to replace the IVR, read up on
@RedFish's posts on the subject.
