This case is designed to remotely mount the AP-4000 module circuit board outside of the case.
It’s popular mount is in the back of the AP-3000
If you need to replace your HDG module or add a Garmin GPS to your AP-3000, this is the solution of the modification. Mounting the box for an AP-4000 module main board outside your radio will take a few minutes.
*Drilling and some mechanical work required for removal and mounting.