The fuel sending unit in my w124 wagon was stuck on 1/4 tank. While in the junkyard I pulled one from another w124 diesel wagon. When I took this one apart to clean it I found what looks like a resistor soldered in the top. I haven't seen anything like this before so I cleaned this unit up and installed it but it doesn't register. I'll take a picture in the next couple of days and post it.

Has anyone seen a sending unit with a resistor soldered in the inside?

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If it ain't broke take it apart and find out why.

1983 300SD, 4 speed
1994 C280
1987 300TD wagon
1996 HD Road King

Ride in Peace Eric Peterson, Harley of Macon

The resistor is there to compensate for the differences between the sedan and wagon tank shape.

This is what allows the same fuel gauge in the instrument cluster to work for either a sedan or wagon, gas or diesel.

Remember this is 80s technology. Nowadays you have a computer in the mix that takes care of the compensation of the shape of the tank on the gauge reading.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Interesting. I filled the tank and it does register but the needle will "jump" every now and then. Would that be a sign of a bad resistor? I think RadioShack sells those, or at least it did.

__________________
If it ain't broke take it apart and find out why.

1983 300SD, 4 speed
1994 C280
1987 300TD wagon
1996 HD Road King

Ride in Peace Eric Peterson, Harley of Macon

Sounds like a bad connection or the gauge going bad.

I would try opening the connector head and giving each contact a very gentle tweak with needle nose pliers, so it gets better grip on the plug pins in the sender.

I would also check the ground connections.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

they jump a bit normally.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

My 87 300D fuel gauge was jumpy below 1/2 tank. I replaced the fuel/oil/temp gauges I pulled from my old 92 190e. No more jumping. When you move the needle to full on the old gauge it drops down instantly. The new gauge has some built in mechanical resistance so it drops down slowly. Think of it as liquid filled gauge that absorbs shocks. I don't know what year MB made the change.

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CENSORED due to not family friendly words

yes ive also noticed that my e300 gauges are damped. i have seen some older cars even w124 and their gauges had no damping.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)