Sounds like the horn was not working for a while before the SIR light came on, is that correct? If yes, check the horn fuse, and if ok, swap out the horn relay with a known good one from inside the fuse panel. Basically, troubleshoot the easiest and safest circuit first.
And it would help to get the SIR (airbag system) DTC to see what problem exists.
If the horn fuse and relay are ok, connectors at the horn are ok, it could be the roll coil connector (aka Sir Clock Spring Connector) in the steering column. But as 4Speed noted it is usually from messing around with the steering column. Also if working on any parts of the SIR (AIRBAG) system, make sure to disconnect the battery first for a minute or two before messing with the components. I have had an airbag blow in my face twice, and it is no fun, and kind of expensive too.
So before ripping the column apart, do some simple steps first.
And if it is the roll connector that is broken, make sure to align it correctly.
Notice: The new SIR coil assembly will be centered. Improper alignment of the SIR coil assembly may damage the unit, causing an inflatable restraint malfunction.
Important: The SIR coil and multifunction, turn signal switch are serviced as an assembly.
Important: If double wire harness strap is installed onto the wire harness assembly and column, you must reuse the holder for the wire straps during installation.
Remove the wire harness strap(s) where necessary.
Verify the following conditions before centering the SIR coil:
• The wheels on the vehicle are straight ahead.
• The block tooth (1) of the steering shaft assembly is in the 12 o'clock position.
• The ignition switch is in the LOCK position.
To center the coil perform the following:
• Rotate the inner portion of the SIR coil clockwise till it stops.
• Rotate the inner portion of the SIR coil counterclockwise 3 ½ turns till the indicator marks line up (2).
• At this time the steering wheel harness (1) should be at the 12 o'clock position.
• This indicates that the SIR coil is now centered and can be installed to the steering column.