Don't call it a bad gauge just yet...The blinking light means your voltage limiter is working and supplying current......Make sure you have a good connection between the bulkhead terminals for the sending unit wire... If that checks out then you can test the gauge and see if you have a range of motion...

Disconnect the gauge from the cluster wiring and use 2 C or D batteries to get 3 volts...Then connect it to the gauge{pos to limiter post,neg to sender post}...If it's good it should come up to about half way or a little better with the sweep...