Replace the "dome" fuse. IIRC that sends the 12v to the clock. If you remove the dash plastic overlay around the gauges and htr controls, you'll be able to easily remove the gauge cluster and check the ribbon connector. It's a cheesy setup and you'll probably find corrosion at the least or burnt up ribbons at the worst. Mine has a piece of wire jumping the burnt up feed to my clock. It keeps perfect time. I have the schmatic on the PC if anyone needs it.
I'll just post it:
89' YJ Larado 4.0L,AX15
05' Grand Cherokee Limited, 2"OME lift and a Hemi.