Horn failure after ignition switch replacement

[JosephJones]

Have you check the connection, It might be because of this. Which switch you have replaced with? Sometimes it may be due to a different configuration of the switch as it does not support the other configurations.

[Jamesp]

I've checked everything

With the new style ignition switch in, the horn works until the switch is turned to the run position

With the original switch in, the horn works with the switch in the off position and works with the switch in the run position.

[911monty]

Looking at the electrical diagrams in the Bently manual there is a change in the horn relay 2001 MY. It appears that the later model for the 7.2 DME may have added a diode and is directional where the earlier is not. I don't have a schematic for the later ignition assembly to compare to, but Maybe try an earlier Relay? Hey Particlewave what do you think