Help with my heated rear window

[Wing Commander]

Right, we had another frost this morning and I am annoyed at my heated rear window not working. I need some help diagnosing things, and for confirmation I am on the right tracks. Car is 1997 Saab 9000.

The details:

12V is present across the window when the button is pressed
There are no broken elements in the window
The earth from the heated window is good, according to the multimeter
The relay energises
The resistance between the relay and the 12V side of the elements is 0.

The output from the relay goes into a fairly hefty wire (it does run near to 30A) but at some point behind the dash, it splits into three - the heated screen, the heated mirrors and the dashboard light. The dash light works with no problems, but I don't think the mirrors work.

Finally, if there is a light frost or the window is misted up, I can see the elements *very* gently clearing in their immediate area, but nowhere near enough to be useful. So it points towards not getting the current through the elements. So there must be a serious resistance somewhere in the circuit somewhere (much higher than the element itself). I just don't know where it is, because of the low resistance measurements I mentioned above.

Any help from anyone??

Thanks

[HellDiver]

Voltage being present doesn't mean there's current present. Could be a bad connection somewhere, probably at the relay.

[Wing Commander]

HellDiver said:

Voltage being present doesn't mean there's current present. Could be a bad connection somewhere, probably at the relay.

Indeed. I measured the resistance between the 12V side of the element and the relay, but in reality I disconnected the cable from both ends and confirmed the cable was ok. You may be right in thinking the actual connection between the cable and the relay may be bad. Will investigate this on the weekend.

[Petrolhead_Rich]

what is the resistance between the two contacts on the window, one could be loose, do you get a clear spot round one of them???

[Wing Commander]

Can't remember the resistance across the element, but will measure on my lunch break. I cleaned up both connections on the element and the connections are good.

[WOO5IE]

Sounds like an HR connection. Probably the relay contacts not passing enough current

Either swap relay or strap contacts out if possible to prove.

[Wing Commander]

Forgot to add - I'm assuming the relay is ok because it's exactly the same as another relay in the car so I swapped them around. Heated window didn't change. Not sure if this rules out the connections betweenthe relay and the wiring though??

[Wing Commander]

Just been out to test the resistance across the element. If taken from connection to connection (the connections are soldered tabs of metal that the wires the connect to) then I get about 0.3 M Ohm. If I measure across the element itself, I get 15k Ohm, which is much more like it!

I will resolder the joints on the weekend and then hopefully I will have a working heated screen! I can only assume that the heated mirrors do in fact work, or there is another unrelated problem with them. Either way, don't really care as they are not as useful as the rear screen.

Thanks all