Norther gas gauge question

[jwn1975]

Hi guys,
I put a new to me cluster in my 69 Chevy. The gas gauge in the old cluster worked fine. On the new to me cluster the gas gauge reads on the 3 o'clock position. When I unhook the ground at the sending unit it goes to the 6 o'clock position. When I hook it back up it goes back to that 3 o'clock position. I checked the ground behind the cluster nothing changed. Please help. I try to manually move the gate back with the cluster apart but it continues to go to the 3 o'clock position