1989 caravan gas gauge

Need help. My 89 caravan gas gauge has suddenly become haunted or worse. When I turn off the key it goes past empty or full and points straight down.

Also at the same time I noticed that all my turn signals are dead.

Fuses are fine and changed flasher unit.

When I turn the key on, the gas gauge goes back up, but dont know if it is showing correct amount. I noticed a wire under the driver side undercarraige that was disconnected and I reconnected it. I need help. Thanks

If the turn signals are dead try disconncting the battery for like 10 minutes and then reconnect , see if that helps at all.

Tried the battery disconnect. No luck. Does it matter if it is positive or negative terminal?