Sending unit and Moeller Fuel Sending Unit Conversion Capsule

I posted this problem in the fuel section but got no help, maybe someone may have some suggestions in this Crusader thread.

I installed a new Moeller fuel sending unit, which is different than the previous sending unit that was installed. This previous unit was the sending unit with a Moeller Fuel Sending Unit Conversion Capsule. Two wires went to the Moeller Fuel Sending Unit Conversion Capsule and two other wires were grounded to the sending unit.

I installed a new sending unit (Moeller) without the Unit Conversion Capsule, it has a center post for positive, and a spade for the negative wire. My thought was to do away with the capsule and connect the two wires so the gauge would read correctly. The problem is the guage is not reading the sending unit, and I have two extra wires not used now, these were the wires that grounded to the old sending unit.

I tried all combinations of attaching the wires and had no luck in getting this to work. The Moeller Fuel Sending Unit Conversion Capsule I had is only a year old, and I think it works fine. The new sending unit was installed correctly.

The new sending unit is: Moeller Product Description: 4"-28" Electric Sending Unit Tank Depth
Product # 035725-10

Any suggestions would be helpful.

I don't know why you have 4 wires at the sender. All you need at the dash is
12 volt + from the ignition switch "run" terminal to the fuel gauge + terminal. The gauge gets its - through the sender.
Wire from gauge "sender" terminal to the screw terminal on the tank sender. Connect the spade "ground" to the battery negative. Your deck fill should be connected to the tank & the tank should be connected (bonded) to the engine via the -
negative battery terminal to drain static electricity, that may be one of the extra wires you have at the tank. There usually is a tab welded to the tank for this or connected to one of the sender mounting screws. As a test if you touch the sender wire to the tank the gauge should go full scale with the ignition switch in the run position.

Thanks, makes sense that one of the two extra wires would be a ground for the tank, but the fourth wire I do not know about yet. The gauge should be working fine,
it pegged when crossing the wires. But I will test it anyway just to be sure. I have the test procedure from Moeller. I will also do a ohm test on the sending unit today.

Thanks for your help.

Your engine block will be your "system negative common".

The fuel tank itself must make a system negative common connection.
The the sending unit itself must also make a system negative common connection.

As rfdlou said, the instrument recieves a variable Negatvie through the tank's sending unit, as to give you the fuel level reading.


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If you have the sending unit listed and a standard electrical fuel gauge, you don't need any capsule.

Unlike what was posted above, I'll express my 'view' differently. There needs to be two connections from the gauge to the sender. These are the two ends of the variable resistor that drive the gauge. Typically, the "ground" side is "shared" with the 12 VDC supply to the gauge...This works fine when the sender is electrically tied to the engine block.

The gauge sounds like it behaves correctly with the key on...so you only need to ensure the integrity of the sender wire and the "ground" wire (between the gauge and the sender).

Thanks, I thought I did not need to capsule which is why I ordered the sending unit with only teo connections. I have not gotten back to solve the problem because it has been too hot down here. I need to see if the sending unit shows OHMs (I have about 1/2 tank of gas now), if it does then I will check the fuel gauge on the dash.

Thanks to all for the help.

Update: The sending unit is showing 62 OHMS, this should be right because I should have under a half of tank of gas. Now to check the gauge, and still need to determine
what to do with four wires when I only need two, but which two is the question, the puzzule is three wires were grounded when using the capsule.

62 ohms should be OVER half full, using the american standard (240 @ E, 33 @ F)....but thats going off memory.

Which two (of the four)? The one that connects to the sender terminal on the gauge and the one that connects to the ground side of the gauge... The others are needed for the gauge but could be part of the grounding system for the fuel fill plumbing - only way to find out is to trace them and find out what is on the other end...