Rear blower motor fuse blows 1999 Cadillac Seville STS

The fuse for the back heater blower blows when I start the engine. It will run perfect with the key in accessory position but as soon as the engines started the fuse blows .. please any ideas what the issue could be. Any help will be appreciated.

The rear blower motor fuse (Fuse #28 10 amp) is the fuse you are describing. As a test for the blower motor circuit, remove the rear blower motor relay(RR BLO Relay). If the fuse still blows you for certain it has nothing to do with anything downstream from the relay in that circuit. Use the provided wiring diagram for reference.

1999 Cadillac Seville Rear Blower Motor Wiring Diagram