Intermittent Gauge function

[sjx40250]

My daughter has a '98 XJ Classic with the Up-Country package. It has several issues one of which is the gauges occasionally don't work. The lights are fine It is always the tach and sometimes the other gauges. It runs fine otherwise.
It has an aftermarket radio with a messing conversion on the wires, but I think the radio is good.

Any suggestions of where to start?

 

[RCP Phx]

It's usually the bus connection at the rear of the gauge cluster, there was even a TSB issued for this.

 

[sjx40250]

So pulling the gauge assembly is the first step. How would I find the TSB and what is the issue/solution?