The oil pressure sensor on my SDL was bad. When you turned the key on, the gauge pegged full scale. I checked the sensor and it measure as an open circuit.

I'm going to put a mechanical gauge on and need an adapter for the 1/8"-27 threaded end on the lube. I've decide to make one from the old sensor. First I removed the housing. Here's what's inside.



It's a simple variable resistor. The wiper moves across the windings of the potentiometer. The wiper is connected to the case and one end of the winding is connected to a wire that goes to the single pin on the outside of the housing.
On this particular sensor, there is an open circuit between the wire and the first winding.



I've disconnected the spring here and rotated the plate to show how pressure will will push on the threaded set screw and cause the wiper to rotate across the windings.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

wow, I thought it was a solid state design

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1981 300SD 512k OM603

It is solid state (no vacuum tubes).

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

That's pretty nifty! I had been meaning to open a failed one I have.......I never suspected it'd be such an interesting thing to behold. Very cool. No wonder they cost $75! Quite an intricate and precise little apparatus.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Thank You.

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'84 300SD sold
124.128

Is there a digital replacement for them?

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine