Greetings and Welcome to Just answer. Lets try resetting the vehicle.
Take both cables off the battery. Touch the ends of one set together for 10 seconds. This resets the entire vehicle and may correct this issue. Try it and see. Let me know.
Do the rest of the dash/cluster lights dimm with the dimmer dial?
yes, I also have an OBD2 that shows no problems when I run that
Ok, then this is likely a failed cluster. The momentary surge when you connected the battery may have been enough to damage the cluster. The 2 options you have are to have your cluster repaired by a speedo repair shop or get a replacement. Check on E-bay. I am seeing clusters on there for 130 or so with a great warranty.
OK. Please reply if you need anything more on this issue.