This compressor mounting location with and Excel Headlight only applies to Softail and Fatboy models of Harley Davidson Motorcycles.
If you have an Excel Headlight installed on your Harley Davidson Softail or Fatboy, the air horns compressor will mount inside the light as indicated in the compressor picture link on the right
Springer - Air horns for Harley Davidson motorcycles
The air horns will use the mount indicated in the horns picure to the right. The running light is disconnected and the air horns are mounted using a rubber shock.
The air horns compressor is mounted in the left-hand saddle bag as indicated in the compressor link to the right.