heated rear window not working

hi i have a 51 plate td5 auto. the heated rear window has stopped working. fuse is ok , my mate who is a mechanic had a quick look at it he has this electric test gismo. he said he was getting a reading of earth from both connections that connect to the heated rear window.and would look at it again in the new year. i have took the panel off the tailgate.a brown and purple wire feed to hrw.as per the wiring diagram. goes into the side of the tailgate and is then covered by the wiring loom. both the wires that connect to the screen seem to be black which i take to be earth wires. i assumed that one connection to the sreen would be earth and the other one live to complete a curcuit. any one any ideas?? many thanks.

I thought that if one line has fault the whole thing doesn't work?

All simple electrical circuits will require at least one power feed and one return.
In a motor vehicle, the power feed is most often 12 volts and the return is earth, ground or chassis, they're all basically the same. Most modern vehicles are connected as negative earth; the negative terminal of the battery is connected to the chassis and the power feed is therefore +12 volts.
With any circuit element such as your rear window heater, testing it against the chassis with a volt/ohm meter will show a low resistance to earth on both connectors until you disconnect both the power feed and the return wires.
You should then measure a low resistance to earth on one of the wires, a high resistance on the other wire, or +12 volts when the circuit is swtched on and a low(ish) resisitance when connecting your meter across the heater element.
One place where the rear window heater wiring can go awry is in the flexible rubber conduit (tube) taking the wiring from the fixed part of the doorframe to the rear door. The regular use of the door can put a strain on the wires causing one or more of them to break. The same thing can happen to wiring in any of the doors.

alan morgan said:

hi i have a 51 plate td5 auto. the heated rear window has stopped working. fuse is ok , my mate who is a mechanic had a quick look at it he has this electric test gismo. he said he was getting a reading of earth from both connections that connect to the heated rear window.and would look at it again in the new year. i have took the panel off the tailgate.a brown and purple wire feed to hrw.as per the wiring diagram. goes into the side of the tailgate and is then covered by the wiring loom. both the wires that connect to the screen seem to be black which i take to be earth wires. i assumed that one connection to the sreen would be earth and the other one live to complete a curcuit. any one any ideas?? many thanks.

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maybe there's a bodge somewhere on the wiring cos one wire in the heater element's plug must be brown/purple... though if the live circuit is interrupted to the element if the plugh is connected there will be earth reading on both terminals(one with higher resistance) cos it closes through the element

see if the mirrors heating is working or not cos they are on the same circuit at the front side, if the mirrors are not working and the fuse is good unfortunately it seems that the relay is gone which is built in the interior fusebox and not replaceable alone