This is a major and common issue on the 1993-1995 LS400.
What happens is the printed circuit board in the instrument cluster develops a hairline crack on the circuit board and as heat/cold causes the part to expand and contract the circuit opens and closes a complete circuit.
Long story short here the solution is to replace the circuit board. This is a dealer specific part and several undred dollars just for the part, to replace requires cluster removal and complete tear down. The retainer screws and internal components of this cluster are very sensitive and fragile (very similar to disassembling a complex computer) and should only be done so by qualified and trained technicians that are familiar with these units.