I have a 94 ls400.. I had the instrument cluster rebuilt.. everything works but the tach, last night it worked for 5 seconds that was the first and last time... I was told the tach worked when shipped.. needle and lights work but tach won't, any suggestions ?? were does the tach get signal from ??? I have replaced both coils....thanks for any help

 

likely either the electrolytic capacitors in the cluster circuit board or else the electrolytic capacitors in the ECM - my tach not working turned out to be the latter one

 

Mine also stopped working a few weeks ago so I gave the dash above the cluster a thump and it sprang back to life and has been fine since.
Have you checked all the plugs and sockets at the back of the cluster as it's a bit tight in there and you may have pulled a connection loose.
Did the tachometer work before you sent the cluster for repair?

 

No Nothing on the cluster other than the speedometer worked..... no lights not gas, temp tach......, now everything but the tach works and at times that will work.... for about 5 seconds and then it goes back to zero.... not sure what to look for, in regards to that problem

 

I can repair any LS400 cluster problems.