79 300sd: location of power window relay? - Mercedes-Benz Forum
 
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#1 (permalink) Old 05-31-2009, 02:57 PM
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79 300sd: location of power window relay?

Hi there,

I'm trying to diagnose the cause of multiple power windows failing on my 79 300sd. Have tested the driver-side window motor (it was fine) and the driver-side console switch unit (also fine).

I'd like to take a look at the relay (or relays) for the power windows but I'm having trouble finding it.

Searched the online wiring diagram but diagram 8 (which covers the power windows) seems to be missing.

According to my Haynes manual (covering other diesel models of the era but not specifically the w116 300sd [which seems to have been produced only for the American market]) there are (in at least one other model) two relays for the power window motors (one for each side?). On the other hand, the wiring diagrams for the US model 300cd and 300td indicate that these models have only one power window relay so my guess is that the 300sd does as well.

Thanks for any insights you might have.

Best regards,

Linus

Last edited by Linus; 05-31-2009 at 03:49 PM.
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#2 (permalink) Old 06-04-2009, 03:47 PM
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They are under the hood in the fusebox I believe. They would be the sqaure ice-cube relays behind the ceramic fuses.
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#3 (permalink) Old 06-05-2009, 10:34 AM
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They are under the hood in the fusebox I believe. They would be the sqaure ice-cube relays behind the ceramic fuses.
Thanks so much. I read something similar about the W126 window relay and had checked my own box but assumed that the W126 had a larger fuse box. Are you saying the ceramic fuse unit has to be removed to see the relay(s)? The relay isn't visible just opening the box.
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#4 (permalink) Old 06-07-2009, 10:47 AM
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I removed the single screw securing the ceramic fuse unit and pulled it up and forward but only could see a tangle of wires. I might just not have been seeing it. Will keep looking...

Last edited by Linus; 06-07-2009 at 11:01 AM.
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#5 (permalink) Old 07-11-2009, 10:43 AM
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There is no relay for the windows on a 116. Its a fuse, switch and a motor, thats it. Theres only wire under that fuse panel.
When you say multiple window failure, which windows are you talking about?
LF & RR windows are on one fused circuit
RF & LR windows are on another fused circuit
check fuses first, they may look fine but may be corroded giving a bad contact. Give them a twist and see if they're arcing.
Are you getting power to the fuses?
Are you getting power to your switches?
Are you getting power out of your switches?
If yes to all above, wiring going into the door at the pivot may have rubbed away the shielding and caused a short to ground. Open and close the door while holding the switch.
If you dont have a test light or a volt meter you will never be able to dianose electrical problems.
Hope this helps, good luck
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