On the way home last night I noticed my fuel gauge was not indicating and appeared completely dead. No low fuel indicator light either. Everything else in the cluster is fine. Tank is full.


I replaced the sending unit a few years ago, with a used unit.


Now on to determine if the issue is the gauge or the sending unit again. Does anyone have an electrical schematic of the fuel indication system? Thanks.

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2012 B Class

1981 300D - Now with greazzer

Does the needle flicker, even slightly when you turn on the ignition key ? .

If not, remove the fuse box cover and look for any gray colored fuses and replace them all with proper copper fuses of the correct ampere rating ~ they're cheap at VW Partshaus' .

Gray colored strip fuses corrode and stop working over time .

often you can gently roll them in situ with your fingers but this is always a temporary repair, better the replace all the gray srip fuses first, them if the gauge still is recalcitrant, move on .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

No the gauge us completely dead. I didn't think the circuit being fused, however the rest of the cluster is OK. I'll check that out. Thanks.

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2012 B Class

1981 300D - Now with greazzer

It certainly _is_ fused, the fuse # is on the card inside the fusebox cover, it's delicate and easy to break so be _gentle_ in removing it .

Each fuse has the raised # casted in the fusebox next to it, sometimes hard to read due to dust / dirt .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

From what I understand, wonky fuel gauge is one of two things:

1. The actual sending unit in the tank.

2. The gauge cluster.

Based on your symptoms, I'd guess something died in the back of the cluster. If something was wrong the sending unit, I'd think you'd have some kind of movement from the needle.

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'80 300SD - '83 240D - '00 E55 AMG - '02 G500

Well its not the fuse, they are all good. It looks like the fuse would handle the entire cluster. Still trying to find a schematic that would cover that circuit.

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2012 B Class

1981 300D - Now with greazzer

Is there a float on the sending unit? I've forgotten but on many vehicles, you can measure resistance as the float level changes.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

If like my 1960's U.S. cars, the most common problem in an old sender is that the brass float develops a pinhole leak and no longer floats.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

It's a composite float and rarely fails .

The sender is directly underneath the first aid kit on the rear parcel shelf, use a stubby #2 Phillips screwdriver to remove the single screw then gently tip the plastic tray up and out, set aside .

Peer in the open hole, there's a square black plastic plug with three wires, wiggle it with the key on and see if the gauge moves .

If not, the sender comes out easily with either a LARGE pair of Water Pump Pliers (nee: Channel Locks) or a 46MM socket .

I've forgotten the wire colors , you bridge two of them to force the gauge , someone here will explain .

The sender is a long aluminum tube with extremely delicate wires inside, if you need to open it to look, use a small pin spanner or, like everyone else including Dealer Mechanics, a pair of pliers to gently squeeze the brass nut's plastic surround *just* enough to where you can unscrew it then the bottom comes off followed by the aluminum tube, revealing the float and delicate wires .

BE GENTLE if you decide to try cleaning the wires ! .

Because the gauge doesn't move at all I doubt the sender's at fault but now you know what to do .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Since neither light nor gauge work, it’s not the sender. Nor is it the cluster. With 99% certainty it’s the ground. The three connections on the sender are ground, float, and reserve light . The float contact will have a variable resistance to ground, this drives the gauge. The reserve contact will connect directly to ground ONLY when the tank is low. My bet, the ground wire is broken or poorly terminated.

So then ground is open at the sender, at the connectors ground pin. Check the connector wires.

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2012 B Class

1981 300D - Now with greazzer

Not necessarily ~ the gauge cluster has a bunch of common grounds so I'd look behind the binnacle first....

The fuses need to be tested in situ using a test light and nothing else first, the comment about fuses from the O.P. sounded like he doesn't fully understand .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Here's the wiring diag you're looking for https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/ETM/82_300.pdf

P 120 you can see the gauge cluster power is not fused. You can do a quick test with the key on, short pin 1 and 2 on the sender connector to pin 3 (ground). The low fuel light should illuminate and the gauge should rise. If not, short pins 1 and 2 to a chassis sheet metal ground..... if it works, the ground wire on the connector is bad. If the chassis ground does not help. Check power at pin 6 ? on C151 (circular connector) on the cluster as well as the grounds.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

My dad always called channel lock pliers “water pumps” I have never heard anybody else call them that...

Air Force?

New Yorker?

Baby boomer...

Just curious if you know where the term is from.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Since the instrument cluster is un-fused, be careful when working on it. Make sure the key is off whenever connecting/ disconnecting the connector/ grounds etc.

I didn't know the cluster is unfused untill looking at this diagram. Jake2tech smoked the wiring on his W124 by not taking the above precautions.

I guess Mercedes designed it unfused because they feel loosing all gauges due to a bad fuse is not a good thing. I think they could have done better with a self resetting circuit breaker.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked