Which style of seven pin connector, RV blade or round utility trailer?
Flashing could be a circuit breaker tripping then resetting. Cause could be over loaded circuit.
Test your trailer using a jumper wire from trailer battery to each of the lighting functions in the trailer.
verify with test lamp that the battery pin on the trailer is going to battery.
Verify ground in connector is going to battery negative.
There should be a circuit breaker in the small box or adjacent to it where the connector cable changes to the trailer wiring system. Make sure it is on the positive cable wire.
