View Full Version : Rear window heater non-responsive.Help!

11-23-2006, 11:02 AM
I recently purchased a used 1989 E32 730ia and now winter is really coming in in Sweden and the defroster/rear window heat doesn't work I must ask help for this as there is no one anywhere near where I live that seems to know anything about these automobiles. I've called BMW in Uppsala but they can't analyze the car over the phone. When I press the button for defrost it lights up and the symbol for rear window heat also lights up but the window heat doesn't come on. I thought that those little wires might be broken somewhere so I had an entirely new back window put in. Still won't work. BMW pointed out that there is an electrical box under rear seat with many relays. All säkringar (fuses) are in place and okay. I replaced the relay that was responsible for window defrost/heat. Nothing happens when I press the button for defrost. The fan/heat works fine for front window but the back window doesn't get warm. I am NOT getting any power to the window wires but jesus what a tangle of wires is connected to this box under the back seat :( Can someone please give me a tip/suggestion on what/where to check next that isn't too complex ? What a site this is..never knew it existed.

11-23-2006, 12:20 PM
On e32s there are two (at least) fuse boxes. One is in the engine bay, and the other as you said is under the rear seat. Check the one in the engine bay to see if any fuses or relays there my be related. If everything checks out that way, then it would be my quess that a wire is loose somehwere inbetween your switch, and the fuse box. Or between the fuse box and the window itself. I have the e32 repair manual (but not on me) so I'll check if it says anything about trouble shooting this problem.

Also, if you haven't done so already, post your question on bimmerforums.com ... they have a much larger 7-series section and many knowledgeable members.

Worst case scenario, you could always pick up a 12 volt space heater and put it in the back window. I know at least some e32s had a outlet in the back. Not a very graceful solution, but would be a lot cheaper then labour at BMW to diagnose the issue.

Good luck!

11-23-2006, 12:33 PM
Thank you Mr. Seven, I am grateful for the help ansering.

11-24-2006, 03:16 PM
Hey Rickster, looked for more info in the repair manual last night. Didn't really find anything all that useful, except you'll be glad to know that the wiring diagram looks fairly simple for the rear window defogger. One thing that did sort of stand out for me is in the wiring diagram it shows some sort of defrost controller, which is located in the back somewhere (near the rear window?) ... I couldn't find any more info on this controller, but it may be something to look into.

11-26-2006, 06:02 AM
Thanks Seven...I pulled off the covers beside the windows and the one on the right..ig your kneeling in the back seat..has nothing to do with heating..looks like different radio band connections/anntena and in the left cover is a small rectangular black (thin) box..on the upper side there is a plug-in..there are two brown wires running to this receptace.one stay disconnected and you can connect either one (both are brown) which leaves one always disconnected. Someone told me that brown is always 'ground wire' in BMW's. I've tried both alternatives and neither one makes a difference. Now I need to find out what the box is/means. It says:contact backreutärvarme but it mabe is just a switch ??

11-27-2006, 12:03 PM
Hmmm, sounds like that box could be what you are looking for. In the diagram there are two wires connected to it, I'd have to look again to confirm. If you've tried all combinations, maybe that piece of the puzzle is just fried? Sorry I can't be of more help.

My suggestion now would be, that since you have all the trim pieces off, just take it over to a bmw shop and ask them what that box is for, they shouldn't charge you anything for that, since you've done all the work so far. Or again, maybe someone on another forum can be of more help?

Let me know what you find out.