Willys Jeep FAQ: Testing Your Sending Unit and Fuel Gauge
Questions & Answers
Questions: My fuel gauge reads full no matter how much fuel is in it or what position the float is in, is this a wiring, sending unit, or gauge problem?
Question By: Hudson on Jan 30 2023 11:36 PM
You need to test your sending unit with a ohms reader. and then make sure your gauges is the proper voltage. Also check your wiring and ground.
Answer By: Willys Jeep Parts Tech on Jan 31 2023 5:44 AM
Questions: Can i just buy the white float? Mine has a crack in it where the wire wraps around... Thanks!
Question By: Chuck Hawley on Jul 11 2022 5:24 PM
Answer By: Willys Jeep Parts Tech on Jul 11 2022 11:21 AM
Questions: What sealer do you recommend on the cork gasket? Thank you
Question By: Carl Marten on May 12 2022 1:19 PM
We typically due not use a sealer there so it doesn't get into the fuel. If you tighten properly it should not leak.
Answer By: Willys Jeep Parts Tech on May 12 2022 10:46 AM
Questions: Can you clarify the Ohm readings for this unit at empty and full? There are two previous answers to this below, and the answers you provided are different.
Question By: Nate Jaros on Feb 20 2022 11:18 PM
7-9 Full and 130-140 Empty
Answer By: Admin on Feb 21 2022 7:10 AM
Questions: I just purchased the 5 hole sending unit for my CJ2A. What wire size will I need to go from the sending unit to the gauge?
Question By: JT Donovan on Dec 8 2021 2:44 AM
We typically use a 12 gauge.
Answer By: Willys Jeep Parts Tech on Dec 8 2021 6:42 AM
Questions: Does the sending unit include the 5 Mounting screws? If not, what size screw will fit?
Question By: Gerry on Jun 23 2020 12:59 AM
B0305 is the part number for the hardware.
Answer By: Willys Jeep Parts Tech on Jun 23 2020 5:45 AM
Questions: Do you have a spec sheet on this sender? I'm troubleshooting my fuel gauge...it's always reading empty (even when full tank of gas) and need to know the ohms it should read at bottom (empty) and up (full). I think full should read 0 ohms, but what sould the empty reading be?
Question By: Mark Ruschak on May 17 2020 8:48 PM
7-9 Full and 130-140 Empty
Answer By: Admin on May 18 2020 5:47 AM
Questions: What is the outside diameter measurement of this fuel sending unit I need to replace mine that is mounted to a rectangle fuel tank on my m38
Question By: Massey on Oct 28 2019 2:02 AM
Please email firstname.lastname@example.org the exact measurement on it you are looking for and we can help out.
Answer By: Willys Jeep Parts Tech on Oct 28 2019 5:37 AM
Questions: Will this work for a 54 willys aero? 6 volt Negative ground
Question By: Michael on May 12 2019 10:44 PM
As long as it will fit into your tank properly and you have a matching ohms reading gauge it should.
Answer By: Willys Jeep Parts Tech on May 13 2019 5:43 AM
Questions: mike, i received this fuel sender and unpacked it. it is being installed in an m38a1 fuel tank, do i need to bend the arm to extend the reach because the m38a1 tank is deeper or leave it as is? thanks
Question By: john mckee on Jan 31 2019 4:44 PM
This is the closest one you can get for the M38A1 in 12 volt. Because the A1 is unique in that it has a extra well for fuel unlike the CJ-2A, 3A, 3B, ect you will know if your gauge is reading empty you have that extra well capacity.
Answer By: Willys Jeep Parts Tech on Jan 31 2019 11:35 AM
Questions: Is this sending unite including the screws for mounting
Question By: Juan carlos on Jan 29 2019 6:00 AM
B0305 is the part number for the screw kit.
Answer By: Willys Jeep Parts Tech on Jan 29 2019 6:01 AM
Questions: Do I need to ground the sending unit? My 53 M38A1 is 12 volt and always registers full even when tank is half full.
Question By: Don Edwards on Jul 27 2018 9:18 PM
Yes, this sending unit for 6 or 12 volt system needs to be grounded. Thanks
Answer By: Willys Jeep Parts Tech on Jul 30 2018 6:03 AM
Questions: What gauge wire is used for this sending unit? Thanks
Question By: Chin on Jun 18 2018 2:57 PM
Answer By: Willys Jeep Parts Tech on Jun 19 2018 6:09 AM
Questions: The fuel tank in my M38A1 looks like it has been replaced. It doesn’t have a hole for a sending unit. Can I drill a hole and add a sending unit and if so what size hole and what sending unit?
Question By: Alan on May 10 2018 11:19 PM
I guess you'll have to drill the hole if you don't have one because how else are you going to read the amount of fuel in the tank. Just make sure you don't let any small pieces of metal fall into the tank. Once that happens, the fuel will push it along the fuel lines and into the fuel pump and carburetor. Thanks
Answer By: Willys Jeep Parts Tech on May 11 2018 5:12 AM
Questions: What is the proper resistance range of this float assembly? I took my inoperable one apart to check the winding and I'm only reading 0 to 35 ohms (empty to full). Even a low resistance float usually reads around 0 to 90 ohms. I doubt this is a 33-240 ohm high resistance unit but I need to know so I can use it with the proper aftermarket gauge.
Question By: Bob Kudamatsu on Nov 1 2017 4:04 AM
7-9 Full and 130-140 Empty
Answer By: Admin on Nov 1 2017 5:47 AM
Questions: I have a 6 screw holes unit down on the tank. Do you have available a 12 volt sending unit?
Question By: Freddy Vargas on Sep 16 2017 1:36 PM
This works on both 6 and 12 volt systems. It works on resistance. You just need to make sure your gauge in the dash is 12 volt.
Answer By: Willys Jeep Parts Tech on Sep 18 2017 5:45 AM
Questions: I have a new gauge and new sending unit both purchased through you and my gauge reads 1/2 full when empty. It seems as though the sender is backwards and should have 1.5 Ohms when empty and 48 ish ohms when full but this one is backwards.
Question By: Reid Nordin on Sep 10 2017 2:24 AM
Please double check the wiring and ensure you have a good ground. They are also adjustable on the tabs that bottom out the arm on the sender. Please call us toll free too and we can help. If you 12 volt you also need to make sure your gauge is 12 volt too.
Answer By: Willys Jeep Parts Tech on Sep 11 2017 11:09 AM
Questions: Will this fuel tank sending work work in fuel tank of an M170? I know that the tanks are completely different. The M170 that I am working on has been converted to 12v.
Question By: Bill Lane on May 20 2017 7:02 PM
It may. As long as you have five screw holes that hold the sending unit down on the tank. The arm length can be modified. Thanks!
Answer By: Willys Jeep Parts Tech on May 22 2017 5:14 AM
Questions: CJ2A new fuel gauge and sending unit-12V system. Needle on fuel gauge is erratic, mostly reads full but bounces around a bit depending on engine speed which makes me think the voltage getting to the gauge may be too high..I have a ground to frame from the sending unit as well as ground to frame on the back of the gauge via the ground post. I've tried a ground to frame from the sending unit as well as having the ground on the back of the gauge connected to the frame-any other thoughts-should there be an instrument voltage regulator or are these gauges designed to run on a full 12 volts? I've checked my alternator, the voltage is as it should be..
Question By: Michael W Stewart on Apr 24 2017 12:37 AM
Make sure you are grounding back to the battery. Call us toll free and we can help out too.
Answer By: Willys Jeep Parts Tech on Apr 24 2017 5:54 AM
Questions: I have a CJ-3A and the origenal sending unit has 6 holes do you have one that would fit that?
Question By: Lane M Ahlschlager on Sep 8 2016 10:29 PM
If your a CJ-3A you should be a 5 hole sending unit so most likely you have an unoriginal tank out of an early CJ-5. I would go with part number: 914850 which is a 6 hole.
Answer By: Willys Jeep Parts Tech on Sep 9 2016 5:47 AM
Questions: My 53 M38A1 has 6 screws this has 5 how will it bolt up?
Question By: Sam on Jul 12 2016 1:13 PM
The M38A1 should only have a 5 screw sending unit installed. Please email photos of your tank to email@example.com something is unoriginal on the vehicle.
Answer By: Willys Jeep parts Tech on Jul 12 2016 9:26 AM
Questions: Will this work to hold the two lever boot down on a CJ 3B?
Question By: Rocky on Jun 5 2013 12:00 AM
B0817 will work perfectly for the retaining ring for the transfercase.
Answer By: Willys Tech on Jun 6 2013 12:00 AM
Questions: My 1950 restored willys jeepster fuel gauge reads one half only when gas tank is full. Car is 6 volt system. Have a vintage wood boat whose gas gauge does the same thing and it is six volts also. What' the explanation?
Question By: Anonymous on Jun 5 2014 12:00 AM
You may need to adjust your fuel tank sending unit and check it with a ohm's reader.
Answer By: Willys Tech on Jun 5 2014 12:00 AM
Questions: My M38 tank is 7 7/8 or so deep. In a reply to another question, you said for an M38A1 they might have to lengthen the arm. Is this arm sized for a 13 gallon tank and does it reach down 7 7/8 inches?
Question By: Matt on Mar 11 2014 12:00 AM
800201 is the sending unit you want to use for the M38
Answer By: Willys Tech on Mar 11 2014 12:00 AM
Questions: I have a 53 m38a1 converted to 12 volt . I have a new tank and just ordered the 640694 fuel sending unit and need to replace 24 v fuel gauge in panel for 12 volt.Which 12 v gauge will fit in panel and how should it be wired to fuel unit in tank. Also, do you know if arm should be extended on fuel unit (bent down) to read accurately in tank?
Question By: Bill on Oct 13 2013 12:00 AM
640763-12V would be the dash gauge you need to use.
Answer By: Willys Tech on Oct 14 2013 12:00 AM
Questions: My restoration project is a 1952 M38. It was converted to 12 volt a long time ago. I have been told that this sending unit will work with the M38 fuel tank. Will the arm have to be lengthened and, if so, how long should it be? Thanks, Don
Question By: Don on Dec 12 2012 12:00 AM
Yes this will be the correct one for you. You can lengthen the arm if you like for that tank but really it will read empty and you will still have some fuel left with is good.
Answer By: Willys Tech on Dec 13 2012 12:00 AM
Questions: where does the wire hook on that sends the fuel level to fuel gauge on a 1946 willyz cj2a
Question By: kenneth on Nov 20 2012 12:00 AM
It goes from the sending unit in the tank to the 's' post on the back of the gauge.
Answer By: Willys Tech on Nov 20 2012 12:00 AM
Questions: my question is I installes anew sending unit and a new guage on my cj3a fuel system, but whene Iturn the power on the guage goes way past full.I PUT WIRE from the sending unit to the frame and I still have the same problem. can you help with this problem.
Question By: jim on Oct 3 2012 12:00 AM
Sounds like a ground issue. Check your ground as well as the wiring in back of the guage to confirm it is not arching.
Answer By: Willys Tech on Oct 3 2012 12:00 AM
Questions: Is this sending unit a replacement to be installed in a 53 M38A1 that's been converted to 12V? If not can you suggest another part number? -Thanks
Question By: Anonymous on Sep 19 2012 12:00 AM
Yes this will match up. On the M38A1 you may need to lengthen the arm if you want it to read accurate.
Answer By: Willys Tech on Sep 20 2012 12:00 AM
I have an earlier M38A1 - the tank is original as far as I know, and has a well that drops below the body. The 5 hole flange pattern is such that the sender fits only 1 way. When I installed the sender, the float points toward the tank baffle and touches it when in the full fuel position. If I make the arm longer the float will run into the baffle way before full fuel. Better to leave the arm alone - the gauge will read empty and not account for the fuel in the tank well.
Answer By: John Behnke on Aug 31 2022 10:00 PM
Questions: just bought '47 cj-2a with this fuel sending unit(item #640694) the the piece that screws into the top of the unit is missing, do I need to replace the whole unit or is that top piece available? Also, is the float cork?
Question By: Bill on May 6 2012 12:00 AM
Sounds like you need a new float. This will do the trick.
Answer By: Willys Tech on May 7 2012 12:00 AM
Questions: does this unit come with new float cant see one in the pic
Question By: garry on Jul 21 2011 12:00 AM
Yes that is correct.
Answer By: Willys Tech on Jul 21 2011 12:00 AM
Questions: do the sending units and gauges have to match (ohms) or will they fit any gauge? reason i'm asking because i need both.
Question By: Anonymous on Dec 19 2010 12:00 AM
Yes, they should be a match. Please call us toll free. We can help. All our gauges and units match.
Answer By: Willys Tech on Dec 24 2010 12:00 AM