I am using a Pixhawk 2.4.8 flight controller with a u-blox 7M GPS module that includes an external magnetometer. The GPS module has a 5-pin connector for GPS and a separate 4-pin connector for the I2C compass. Since Pixhawk requires a 6-pin GPS port, I replaced the original 5-pin GPS connector, after which the GPS began functioning correctly. I am able to obtain a stable GPS fix in under 20 seconds, confirming proper power and UART communication. However, the external compass connected via I2C is not detected in Mission Planner (Setup → Mandatory Hardware → Compass). Only the internal compass is listed. The external compass is enabled in the full parameter list, the I2C wiring has been verified for continuity and correct pin order, and the GPS/compass module is mounted approximately 10–12 cm above the base plate to minimize magnetic interference. Despite these checks, the external compass does not appear or respond, leaving only the onboard compass usable. Has anyone encountered a similar issue with Pixhawk 2.4.8 and u-blox 7M external compasses, or can suggest additional diagnostics or common causes such as I2C address conflicts, power limitations, or connector pinout mismatches?