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ScarboroughSeadog



Member Since: 21 Jul 2022
Location: Scarborough
Posts: 110

United Kingdom 2013 Defender 110 Puma 2.2 DCPU Keswick Green
24V Lightweight 3 Series fuel tank misreading......
This has become a niggle.....

Late model (1979) 24V twin tank- no voltage regulator on these models. Just replaced fuel gauge and one of the lucas switches on the changeover tap, and now I have a fuel reading at least. BUT both tanks read 1/8 full when empty (they read full when full). Its not to do with the position of the sender float (which is at the bottom of the tank). The gauge returns to empty when the ignition is switched off.

Any thoughts on what the prob could be? Both tanks are well earthed.

Thanks
Post #984715 7th Mar 2023 4:35pm
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blackwolf



Member Since: 03 Nov 2009
Location: South West England
Posts: 16808

United Kingdom 2007 Defender 110 Puma 2.4 DCPU Stornoway Grey
You may need to adjust the coils in the gauge. If both tanks display the same quirk it suggests that the gauge is at fault. The classic gauge has two coils which can be adjusted with respect to the magnetised pointer, and it is likely that the "empty" coil is further away than the "full"coil. It's a fairly common issue on Series 1s and vehicles of a bygone age (and I am assuming that the same type of gauge was used in 1979).

This site gives the basics.
Post #984717 7th Mar 2023 4:49pm
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ScarboroughSeadog



Member Since: 21 Jul 2022
Location: Scarborough
Posts: 110

United Kingdom 2013 Defender 110 Puma 2.2 DCPU Keswick Green

Click image to enlarge

Thanks- will have a look. Although the back of my 24V gauge looks like this- not sure it can be adjusted.
Post #984718 7th Mar 2023 4:55pm
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blackwolf



Member Since: 03 Nov 2009
Location: South West England
Posts: 16808

United Kingdom 2007 Defender 110 Puma 2.4 DCPU Stornoway Grey
That may be too modern for my type of calibration! There may be some similar jiggery-pokery available though.

Bend the needle?
Post #984719 7th Mar 2023 5:12pm
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ScarboroughSeadog



Member Since: 21 Jul 2022
Location: Scarborough
Posts: 110

United Kingdom 2013 Defender 110 Puma 2.2 DCPU Keswick Green
It’s the correct 24V part- direct part number replacement for the old one.
It has (and should have I believe) only 2 connections to the gauge itself- the cluster housing is earthed.
I’ve just noticed that the gauge reads full when the tank switch is in the middle (selecting neither tank). Pretty sure it should read zero. Any thoughts if that points to a particular fault?
Post #984742 7th Mar 2023 8:54pm
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blackwolf



Member Since: 03 Nov 2009
Location: South West England
Posts: 16808

United Kingdom 2007 Defender 110 Puma 2.4 DCPU Stornoway Grey
Missing earth connection.
Post #984762 7th Mar 2023 10:34pm
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ScarboroughSeadog



Member Since: 21 Jul 2022
Location: Scarborough
Posts: 110

United Kingdom 2013 Defender 110 Puma 2.2 DCPU Keswick Green
The cluster housing is earthed at each securing bolt- but one of the bolts has two earth connections (which seems odd). Should one of these be earthing the fuel gauge directly? (The oil and water temp gauges are not earthed directly)
Post #984764 7th Mar 2023 10:55pm
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blackwolf



Member Since: 03 Nov 2009
Location: South West England
Posts: 16808

United Kingdom 2007 Defender 110 Puma 2.4 DCPU Stornoway Grey
Oil and water gauges are probably single coil instruments. The fuel gauge I would expect to need an earth connection.
Post #984769 7th Mar 2023 11:25pm
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ScarboroughSeadog



Member Since: 21 Jul 2022
Location: Scarborough
Posts: 110

United Kingdom 2013 Defender 110 Puma 2.2 DCPU Keswick Green
Always good to finish these things off with a conclusion: replaced a faulty fuel gauge, replaced a faulty Lucas switch. All now working perfectly but there is an interesting issue with the senders. I have 3 senders marked TB1114-001W. This is the correct part number. One is brand new, one is say 10 years old, one is say 40 years old. Only the 40 year old one reads correctly (ie empty at empty). The other two newer ones read 1/8th at empty. I can only think the more modern parts have a different resistance scale? Fortunately with a repair made to a snapped spade connection I was able to use the original 40 year old part and all is working perfectly. Bit of a mystery though.
Post #986188 20th Mar 2023 1:51pm
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ScarboroughSeadog



Member Since: 21 Jul 2022
Location: Scarborough
Posts: 110

United Kingdom 2013 Defender 110 Puma 2.2 DCPU Keswick Green
Final thoughts after a helpful suggestion on anther forum: These senders cover a few different set ups, and hence supply to different gauge decals etc. My particular (dated, less common) set up is an anomaly as far as these senders go. I suspect the sender is designed to work alongside a more modern gauge decal set up- with a red block 'empty' position which mine doesn't have.....
Post #986331 21st Mar 2023 3:56pm
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