Heated rear window

Does the heated rear window need to be below a certain temperature to function? My dash switch works (power on and off), but I don’t know if the window is heating. The average daily temp in my area is between 50 and 85.

Bob (87 XJ 6 III)


I’m not aware of any limiter, but physics would suggest that it only works if the rear window is either frozen or misty. Other than that you’d feel a functioning HRL only at low temperature with the palm of your cold hands. In my SII car there is a double indicator: one is the light at the push button, the other is the light in the tach (speedo?). The latter one should only go on if the HRL is powered.

My SII HRL works, but much slower than modern cars, maybe also due to the poor support by internal heating/ventilation.



75 XJ6L 4.2 auto (UK spec)

I use the palm-of-the-hand method of checking, as mentioned. Or, turn the defogger on and wait a minute or so. Now breathe heavily on the glass where the grid wires are. If the wires are heating the glass you’ll see evidence. The ‘fog’ will disappear quickly from the hot grid wires but linger a bit longer where there is no heat


There is no temp limiter, Bob - it should heat whenever the switch is ‘on’…

As a addition to the other good suggestions offered; measure battery voltage and turn the switch ‘on’ - there should be a perceptible dip in voltage if the window draws power.

There are various reasons why it would not - to be explored…

xj6 85 Sov Europe (UK/NZ)

Nothing very sophisticated, but it has a delay relay that turs the heater off after 15 minutes or so.

First thing is to check if the tabs that the cables attach to are not boken.
Second, check continuity between the two tabs .
Third, check if they get 12v and ground.