In article ,
"Dave Plowman (News)" writes:
Yes. The original is a sort of fibre pad with wide tracks on it - rather
like a PCB using something other than copper, and is just glued on. Seems
modern mirrors have the element built in like a heated rear window.

In a similar situation where I wanted to heat a panel, I
epoxied a chain of resistors on the back. Each one is quite
low power. You will have to be careful of water ingress and
electrolosis thought.

--
Andrew Gabriel