So... I've got a 2005 Suburban with some issues. The speedometer and tach jump all over the place along with random warning lights abs anti theft battery ... sometimes they guages go dead. Headlights will dim a little then get brighter . A/C is a little sketchy but I think that's a different issue. I did swap speedometer control panel and it still does it. Would really appreciate any thoughts. Truck runs great otherwise.

 

I'd start by cleaning all the battery cable connections, ground connections, alternator connections, etc. Get them all clean/shiny metal.

 

Thanks cusser...cleaned all the grounds i could think of with no change. Someone mentioned a possible harness issue?

 

Someone else mentioned that it could possibly be a bad PCM? appreciate any thoughts