fuse is good, replaced temp control, can hear a click behind glovebox. is there a relay there? 99 grand prix

check the plug at the back for power, could be an open trace in it

I agree....Check for power AND ground at the grid on the rear window....

where do I find the plug

Rear defogger has to be "on"....

You will have to remove the interior trims on both sides of the rear window......usually the passenger side is power in, and the driver'* side is the ground........attach your test light to both sides to see if you have power......if it doesn't light, attach light to the left side and and other end of light to a good ground.....if it lights, you have a bad ground on the other side.....some grounds have a black ground module, and I have seen the connectors coming out melted...

If it doesn't light, then you have to chase that circuit back to the control head.....more often than not, it'* a bad relay, or it can be a bad contact in a harness connection(for example, in C200), that has actually heated up and melted the plastic surrounding the connection....also check your rear defogger fuse....

thanks. will let you know what happens