lrp competition speedo

[D34no]

Hi i have just bought a secondhand lrp competition esc i wired it as i have all my other speedo and powerd it up but forgot to plug the sensor wire in only noticed when the motor got very hot and started sounding rough
Anyway should this happen if the sensor wire is not pluged in or does it sound dodgy as i dont want to fry another motor and waste £70 again
And has anybody had any dealings with lrp over the warranty as they have a lifetime warranty