E30 fuel gauge warning lamp illuminated but is full, sending unit or ground nut?

[formyhealth]

Hey so I noticed before I changed my fuel pump that my gas gauge on a 1991 318is was acting erratic, the low fuel warning light is on regardless of tank level and the gauge register anywhere from empty, to half to full. Is this a fuel sending unit issue or a grounding nut issue on the cluster? Maybe a cluster issue not relating to the ground nut? Also the temp sensor is also erratic but I noticed if I give the dash above the cluster a sharp whack that the temp gauge acts normal for a minute or two (doesn't do anything for the fuel gauge though)

Here's a picture:

[Darky]

More common would be the screws on the back of gauge board are loose or the Si board batteries are stuffed or need charging!

[formyhealth]

Cool, I was leaning towards ground nuts/screws on the back, I'll tear into it and report back with what I find.