1990 Legacy tachometer quits working

Just purchased a 1990 Legacy AWD. At cold start up, everything works fine.After reaching operating temperature (sometimes a little longer) tach, gas gauge and cruise control cease to function. Even if I stop the engine and restart, these items will not work until after vehicle is cold. Then everything works fine again. Anyone know if there is a relay or if possibly the cruise control servo may be causing the problem... or any other things to look for. Thanks.