Since my indie changed out my rear pads and rotors my sensor light keeps coming on, he has put a second set in but the light came back after about 2 weeks of driving.
Could it be that the plastic sensors aren't up to the task as l believe the oem ones are metal.
My indie suggested to disconnect them if it happens again.

 

Are you talking about wear sensors? I see they are around 6-10 depending where you look.
S99661234700

 

Yes that's right, brake wear sensors.

Had 2 new sets and keep getting the light on the dashboard after about a week or two.

Just searched your part number and they appear to look the same.
http://www.autoatlanta.com/tinyresul...=550&width=875

 

I would check connections first, did your mechanic give a reason for replacement.

 

The second time he took off all 4 wheels and checked everything, he said the plastic was melted on the new sensors. I do drive it fairly hard through the hills but no different to before.

 

That should not happen, I would buy OEM and install them myself or have another shop take a look and have them repair.