Did you ground the wire and watch the gauge? When grounded the gauge should read full hot. If it doesn't we can assume a bad gauge since it has a new wire. If it does then we need to check the sending unit with an ohmeter. Cold it should have resistance. Record that value. Warm the engine and check the resistance again. The value should be lower. If there is no resistance or the resistance is not changing right you need a new sender.
