For mPTX transponder operation refer to the instruction sheet supplied.

MRT mPTX and PTX (NS) transponders are compatible with all AMBrc

systems and the new RC4 system. [old PTX Read Article PTXTIU0117]

Polarity of plug connection can be reversed without problems, but when

resoldering power lead wires to mPTX circuit board check the polarity.

Fast flashing LED - refer to instruction sheet supplied with transponder

The instructions describe what the LED flashes are indicating, it's warning that the location of the transponder is weakening the signal (nothing to do with changing to the ALT ID). The signal is still being transmitted, the laps will still register, but some may be missed due to the attenuated weakened signal. It's not a good idea to mount a transponder direct on an alloy or carbon fibre chassis, it should be mounted either above or ideally off to the side of the chassis using a transponder clip or mount. It's ok to leave it in it's current location, but it would be better to relocate to stop the warning flashes and maximise the signal received by the decoder.

Article ref: MPTXOB0317