i am a newbie so please bear with me. from the start: went to change speedo backlight bulbs ( mine are 2721 btw,not 94or 74) .put it back together speedo 15mph slow, tach 750 low.pulled clear lens adjust needles while running.all good. stop and start motor several times still good. park truck come back later to find needles have "fallen" back below zero(no pins to stop them) again. same fail repeated several times. totaly baffled

 

Reads like a loose ground in the instrument cluster, you fixed the symptom then the ground got better.

 

not sure how to go forward. disassemble instrument cluster-look for bad connection. just replace it. hard to think i ruined it changing a bulb. the 2 plugs look solid .the little wire in the bottom looks fragile(not that i know what it is or how it comes off)