Normalizing a list with both positve and negative numbers to the range [-1 1]
You can do this yourself or use a library such as scikit-learn which has a MinMaxScaler.
data = [-518.8134, 480.1884, 160.4761]

# manual scaling
scaled = [-1 + 2 * (x - min(data)) / (max(data) - min(data)) for x in data]
print(scaled)
# [-1.0, 1.0, 0.3599364886029235]

# using scikit-learn's MinMaxScaler
from sklearn.preprocessing import MinMaxScaler

scaler = MinMaxScaler(feature_range=(-1, 1))
scaled = scaler.fit_transform([[x] for x in data])
print(scaled)
# [[-1.        ]
#  [ 1.        ]
#  [ 0.35993649]]