APM telemetry port, Vcc pin voltage drops under load.

I have the APM 2.6 board. I want to power an external device (an MCU) using the telemetry port pins (which is basically a UART interface). The Vcc pin of this is rated at 5V, as i see with my multimeter. The MCU i want to connect is rated at 3.3V so i've made a resistor divider to adjust the voltage accordingly.

I see that the open circuit voltage is fine at 3.35V. However when i insert the device the voltage drops to 0.647V! I don't know what is wrong with it. My device draws much less current than the 3dr telemetry module.

I've done some other tests and i plugged the Vcc pin of the telemetry port to a breadboard, then stuck an led and a resistor and still the Voltage dropped to 2V (from 3.35V!). Could someone tell me what's going on, or just provide any info and knowledge that may help? The telemetry port of my APM works just fine (at least the Tx, Rx and ground pins). But what could be wrong with the Vcc pin? Why does the voltage drop so much when i connect it to a load?

I would appreciate any help on this issue. Thanks in advance.

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