Maybe something is shorting the horn relay in the RCM?
The horn relay fuse is #6 in the picture. Try taking that out and see if the horn stops.


FUSE # AMPs USAGE
1 15 Traction System Relay
2 15 Oxygen Sensors, Air Pump Relay, EVAP Purge Solenoid, Charcoal Canister Shutoff Valve, Air Pump Switchover Solenoid, EGR Solenoid (except SRT), Supercharger Clutch (SRT), Short Runner Valve Solenoid (except SRT)
3 15 Power train Control Module, Fuel Injectors, Camshaft Position Sensor, Fuel Pump Relay
4 40 Air Pump Relay
5 15 Fuel Pump Relay
6 15 Horn Relay