My speedo, fuel and coolant gauges work, but not the other instruments. Bad ground?
She's an '85 XJ6. Fuse in #4 spot good.
Any advice would be most helpful.

 

Behind the wood dashboard there is a sheet metal backing and the ground is fastened to that so all the gauges have he same ground. So I'm pretty sure you can rule out a faulty ground. Jaguar fuses are notorious; did you use a test light or multimeter to verify current on both ends of the fuse?

 

baws,
Take a look at this schematic of your gauges and see that they are provided 12v from fuse #4 on two different circuits. The -) and (- in the G (green) wire indicate a pin/socket push connector, notorious for corrosion and poor fit. If you take the speedo and tach out of the dash you can probe the G wire (key on) and/or possibly see the connector. To uncover the remainder of that circuit, the under-dash panel may have to be removed in order to see the wiring farther up under the dash.

Speedo/tach removal: push in on the bezel and rotate the instrument CC about 1/2", they will slide straight out toward the steering wheel and expose their wiring connections. If you need to completely remove the instruments, I suggest taking a good picture of the wiring lay-out or draw a diagram to help put the wires back in the right places. Reinstall the gauges by reversing the procedure.

Have the gauges ever worked during your ownership? Has something been done in or around the dash that might coincide with their failing?

Good luck.

Dave