According to the shop book the terminal on the left is the sending unit The right side is the positive.
Wait ! I don't think that's right ~ please look in my older posts for detailed fuel gauge head wiring information . Connecting it wrong will destroy it before you can blink .
I'm looking at the back of the original gauge pack that I pulled out of my '50. The left terminal (looking at the back) has a red tag on it that says: "Connect sender wire to this terminal. WARNING If hot wire touches, sender will be damaged" So, at least on this gauge pack, the hot wire from the ignition goes on the right terminal and the wire to the sender is on the left.