While waiting for my new primer pump, among other parts, I'm working my way down the "to fix" list.

The next item is the rear defroster.

I have the pull knob that energizes (but the relay doesn't click), so I know that the rear window wasn't a salvage yard add on.

The two wires are dangling in the trunk from the PO having a high school votech class paint it a few years ago. They probably disconnected it to remove the rear glass and didn't bother wiring it back up.

What did those kids disconnect and where do I find it? I don't see anything obvious. Each wire has an eyelet, like a ground lug, if that helps.

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1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

I believe (if memory serves me correct) on that car they connect behind the backseat. They should route through a grommet in the rear firewall. Pop the top portion of the backseat and see if there are two junction blocks with phillips head screws. Good luck.

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Cars:
1993 400E
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1985 300D Turbodiesel w/ 688,000 Miles On Original Eng/Trans
1979 300SD
1977 Euro 6.9
1967 230S IMA Universal Wagon
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Thanks! It's now wired up.

However I have 0V at the connector block. The knob lights up so that would imply that I have power at the switch.

Bad relay? Where is the defroster relay and how would I test it?

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1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

Check and clean the "earth/ground" for the defroster. They are susceptible to rusting due to rear windscreen water leaks.

Thanks, Mike, for the tip.

But I think that's good. If I understand you, the earth is a shared ground for the rear lamps (or some wire bundle headed that direction) and is hidden behind the rear seat, driver's side.

In any event, I think there should still be voltage at the relay and it should click even if there was a problem downstream, no?

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1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.