Misunderstanding MOSFETs

[BackwardsLED]

Hi all,

I'm trying to control a neon flex strip using a MOSFET to increase my board's signaling out from 3.3v to 12v.

I've already fried a board by misunderstanding the MOSFET, and all the volt-meter testing I've tried since isn't making sense to me. As per the spec sheet, the MOSFET ordering is Gate-Drain-Source. I believe:
* Gate is the signal that turns output on/off.
* Drain is the higher voltage input I'm trying to switch
* Source is the output to my LEDs

However, when I try this, there seems to be only ~3v flowing out the Source pin of the MOSFET (worse than the original 5v input I'm testing with). What am I doing wrong?

Attached is an approximation of the circuit diagram. I wasn't able to put in the right board, power is 12v not 9v, and the LED strip only has 3 inputs, so please mentally correct those items :)

EDIT: originally I mentioned backflow into the Gate pin. That seems to have been an error while I was trying to get the correct output voltage, and may have switched wires around.

[adafruit_support_bill]

Those 'neon' strips do not need (or want) 12v for the signal line. Use standard logic levels for the control signal.

And N-channel MOSFETs are best suited for low-side switching. For high-side switching as in your circuit, you would want a P-channel device.