heated mirror electrical

Maybe someone can shed some light on this for me. I had my driver side heated mirror not working but the other one was. So anyway I took it apart and found 12vdc coming in but the other side of the mirror post was 0vdc so I checked for continuity on the mirror by itself, it was ok. If I put the 12vdc source on the mirror and not the ground I could check the post for the ground and it would have 12vdc but as soon as I connected the ground wire to the mirror the post switched from 12vdc to 0vdc again. So I reran the ground wire to another ground and that fixed it but Im just stumped on why this happened. Because If the ground wire was broken/shorted what have you, the wire and post should still have 12vdc because it is no being grounded. Im usually very good with electronics but this stumps me.

Any input would be great.
Thanks

I had the same problem, had to replace the mirror

Maybe someone can shed some light on this for me. I had my driver side heated mirror not working but the other one was. So anyway I took it apart and found 12vdc coming in but the other side of the mirror post was 0vdc so I checked for continuity on the mirror by itself, it was ok. If I put the 12vdc source on the mirror and not the ground I could check the post for the ground and it would have 12vdc but as soon as I connected the ground wire to the mirror the post switched from 12vdc to 0vdc again. So I reran the ground wire to another ground and that fixed it but Im just stumped on why this happened. Because If the ground wire was broken/shorted what have you, the wire and post should still have 12vdc because it is no being grounded. Im usually very good with electronics but this stumps me.

Any input would be great.
Thanks


You were reading a voltage drop. The mirror was using up all of the 12 volts. With a sensitive meter you probably would have read a 0.1 or less. You have a good voltage input, a good ground, and a bad mirror.
Mfmiller