Series 3 fuel sender unit problem

Hello , I am looking for some help / advice ? I have a series 3 109 military with twin fuel tanks under seats , I have recently restored it and one of my last jobs was to replace sender units . I ordered 2 (flat metal top with one spade connector on - same as the ones I removed) but I just can not get it to work ? ,
I have serviced all switches and it is all working good , the problem is the gauge just goes to full all the time regardless of float position , I have disconnected all wires , it reads empty , earth the wire and it goes to full , so all good ? , but when I connect to sender it goes straight to full ? on both sides ?? , I think I have tried everything , but any advice would be appreciated ? thank you Joe

There is a voltage stabiliser behind the dash that regulates voltage to the gauges. It is a silver coloured, rectangular metal canister about 2 inches long. If this is faulty it will cause the fuel gauge to misread.

Col

Here's a thread where this issue has been discussed:

https://www.landyzone.co.uk/land-rover/sender-unit-fuel-gauge-issues.360126/

Basically, the Smiths gauges in the military Ser 3 can be troublesome. They need to be earthed properly or they will read high, but they also suffer from internal faults and sometimes replacement is the only option (assuming you can find one ).
First thing to check is that the gauge earths are good both on the back of the gauge cluster and within the cluster itself.

Hello, OK thank you for the advice , whilst out today i called into our local dealership and discussed it with them , they agreed about voltage stabilizer and supplied me with one , I have just got back , removed dash and there is nothing behind clocks ? is there another place the stabilizer can be stored ? , mine is very late series ( 1984 ) if that makes any difference ? thank you Joe

Joe, assuming you have the Smiths gauges (3-way cluster with fuel, oil temp, water temp) then they don't use a voltage stabiliser. But while you're in the dash, check that all the earth connections are clean and tight.

Ok , my gauge has fuel gauge , temperature gauge and one blank in the right hand circle , and oil pressure is a single light in the other circle/speedo , thank you Joe

If your gauges look like this (with a blank instead of the oil temp) then you have the Smiths gauges. Check also if they say "SMITHS" at the top. Most of the military Series 3 had these gauges fitted. They are a bit different to the Jaeger gauges fitted to most non-military LR. The Jaeger gauges are more robust but they are slow to respond and need a voltage stabiliser.

Hello, Yes that is the one , it has smith on it and yes the oil temp is blank . I have just checked all earths on back of dials , added a earth to be sure and still the same , thank you Joe

My gauges are the smiths but I do have a voltage stabiliser. It is screwed to the bulkhead behind the rats nest of wiring.

Col

Voltage regulator screws to the back of the speedometer so that it is earthed.
Fixing screw can be seen in this pic

Blackburn said:

Voltage regulator screws to the back of the speedometer so that it is earthed.
Fixing screw can just be seen in this pic

Click to expand...

Mine ain't like that, I wonder if a previous owner added the voltage stabiliser in an attemp to cure a wayward gauge. When I got it, the fuel gauge didn't work due to a bad earth at the sender.

Col

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Colthebrummie said:

My gauges are the smiths but I do have a voltage stabiliser.

Click to expand...

Strange . In theory the Smiths gauges don't need a stabiliser - the design compensates for changes in input voltage - but I guess it's harmless to use one. Mine don't have the stabiliser and are actually quite accurate (at least by Series 3 standards). But over the past few years I've replaced both the fuel gauge and the oil temp gauge as they had failed internally and others on this forum have also had problems with these Smiths gauges.
It's possible to dismantle the gauge cluster and clean the internal earth connections. But if that doesn't fix the issue then it's likely time for a new gauge

Ok thank you everyone for there information, I think I have decided it is the gauge ? , after trying everything else i dismantled cluster and removed fuel gauge , I have then used the fuel tank wires on the temp gauge as a test and it seems to work fine ? , I have just ordered a new gauge (not cheap) and will let you know how I get on when it arrives ,thanks again Joe

New gauge? Expensive indeed! Well, at least you'll know it's fine! Probably the best solution.

Thank to everyone for there advice , I have now sorted it . I could not get the smiths gauges to work ? I had new gauge , new sender and new voltage regulator and it still reds full all the time , new earths / extra earths still reads full !!! . set it all up on bench with separate supply , still reads full !!! , so I gave up and bought a second hand Jaguar dial , connected it up and it all works fine straight away ? so I am not sure what was happening with the smiths gauges ? but it is sorted now , thank you Joe

This is an interesting threat. I’ve got a S3 83 petrol swb. It used to be a diesel. Since Changing to petrol and changing the sender unit it doesn’t read properly. I have Smiths dashboard, but it doesn’t have oil pressure/ temperature only water and fuel readings. It slowly reads inaccurate; if I fill the tank the gauge reads on third fuel.