It's helpful when you say "the fuse" if you specify which one. There are three associated with the power windows. Do you mean fuses "a" and "b" that control front right\rear left and front left\rear right, respectively? I presume no, since you say "fuse" singular.

So you probably mean fuse 12. This provides power to the relay.

Yes, there's a relay. If Funola knows it's on the wheel well, I'll defer to his experience; but the electrical service manual says it's behind the cluster.

One more question: what's the key position when you're testing? The relay only closes in Run (position II) or start. ACC (position I) doesn't close the relay, so no power to the switches.

To isolate the door wiring, try applying power across pins 3 and 4 on the front switches; or pins 1 and 2 on the rear. Of course there are no rear doors on a CD, so the "mangled accordion" won't be a factor there.

I am going by memory from more than a year ago when I last worked on the pwr windows on my 83 300DT. If the FSM says the relay is behind the cluster, then I am clearly wrong and I apoligize.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

No slight intended. I added the reference to location behind the cluster in case it wasn't on the fender in order to help the OP with additional troubleshooting info.

I'm citing a 1982 electrical manual I haven't pulled the relay behind the cluster. And the manual isn't perfect - it has 4 pages of errata that correct other errors. My favorite is the correction for the coupe seat back locking diagram: "Seat back locking safety mechanism not shown at all."

Actual BTDT can be more helpful than the book.

Maybe it's time for a "name and locate that relay" thread/sticky. Photos and FSM/BTDT references mandatory.

Now we noticed another issue which I think is related. The car no longer supplies power to the starter relay. I dont think its the NSS. Also this morning the power windows worked momentarily so I'm beginning to think its the main ignition relay or whatever relay energizes when you switch on the ignition and then powers everything else. Is there such a relay in the dash? Possible ignition switch?

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1981 300SD 512k OM603