My '94 LS400 has a problem with the dash lights. They do not come on (light) until they warm-up. It can be 2 minutes to 30 minutes before the dash lights illuminate. It seems to be a function of cold and wet. The colder and more wet it is outside, the longer it takes for the dash lights to illuminate.
What will fix this?

 

Read the second "sticky" item in the LS 430/400 section. You will learn more than you ever wanted to know about this problem.

The good news is that there is a fairly inexpensive fix for the problem. The bad news is you have to remove the dash display in order to get it fixed.