Series 3 Sender unit/ Fuel gauge issues

NjHall · May 27, 2020

Hi all, I'm just getting to grips with my 2.25Ltr Diesel Series 3 (109 military)

I've got a problem with the fuel gauge reading full all the time, on both tanks, so thought i'd take a look at the sender units and found:

Sender unit on the Passenger side has 2 connections. One with a broken wire and the rest of it nowhere to be seen. The float works fine.

Sender unit on the Drivers side tank only has 1 connection. Inaccessible for checking the sender float without some graft!.

And then there's this mess:

Has anyone got a wiring diagram, or can give me some direction with what to try!

Cheers,
Nick

steve2286w · May 27, 2020

I’ve got twin tanks on my series 3 diesel but don’t have the military changeover switch
I have two terminals on each sender
One is for the low level light Possibly the outer one
You can test by earthing them
I think I have connected the outers together so red Light can come on When either tank low
The gauge normally reads drivers tank until I press switch to read pass tank
I assume your change over lever also switches the senders

NjHall · May 28, 2020

Hi Steve,

Thanks for the reply, good to know what the second connection is all about! As far as I know the lever also changes which sender reads, due to the wiring going into the lever housing. How would I go about earthing them?

Cheers,
Nick

ExMil109 · May 28, 2020

Have a look at the wiring diagrams on the Lightweight website:

http://www.land-rover-lightweight.co.uk/LRL M.html

Basically you have a green/black wire from the gauge to the tank changeover switches, then a light green/red one to the RH tank sender and a light green/grey one to the LH tank.
As Steve said, the other terminal on the sender is for the warning light.
If you disconnect the green/black wire from the changeover switches and the gauge still shows full then either the wire is earthed somewhere or the gauge is faulty. If that checks out then the problem is either with the changeover switches or the senders themselves.

NjHall · May 28, 2020

Hi Exmil,

Thank you so much for sharing that diagram! It has made the world of difference for my understanding.

I’ve disconnected the Green and Black wire from both sides of the switch and found that the meter then slowly falls to empty which is great... So I presume the meter is okay and the cable isn’t earthing.

That leaves the senders and the switches! So, do you think this is more likely to be the senders/ poor cables or the switch? Or is there any way to tell... Like directly connecting a sender to the meter?

Thanks again,
Nick

steve2286w · May 28, 2020

I would bypass the switches with a flying lead connected the the gauge green black then directly to each tank in turn
This should then read the correct level in both tanks or rough level ( as they can be a bit out)

Then need to check each switch with a resistance meter to see how they work and work correctly to be fair it looks like it could do with a good clean and new wires

steve2286w · May 28, 2020

Just found this , the pic below shows how the switch works , in the middle of thread is a plunger so by pressing this in it will either make or break the connection so a lever on handle when moved will operate this so switch position may need adjusting if it’s not reaching

NjHall · May 28, 2020

Fantastic stuff Steve,

The pair of you have been massive help! I'll hook up each sender to the gauge to make sure they are operational, give everything a clean and revamp, then check out the switches!

Cheers,
Nick

ExMil109 · May 28, 2020

Good luck with the switches! You might find one of them is shorting to earth, or they may both be stuck on, which will put both senders into the circuit at the same time and make the gauge read high.
Actually, this job is on my to-do list as well. I bypassed the switches to get the gauge to work and made a note to dismantle and clean them up. Of course, that was long ago and it hasn't happened... But I only have one tank fitted at the moment, so the changeover valve stays in one position

TheMegaMan · May 29, 2020

Don't want to hijack the thread, but I'd like to ask a few related questions, if I may.

Just refitted my tank (single, under the drivers seat) and so testing the gauges for the first time since wiring the new chassis. And with a completely empty tank, I'm getting a reading of just under half a talk...so obviously a bit of an error in there. I can live with a false 'empty' for now, and I'll see what happens when I fill the tank up, later,

But something I've just noticed is that I have a single (green/brown) wire from the sender tab to the gauge. There is no obvious good earth to the tank. And I've painted it. Now, I assume that if the tank isn't earthed at all, then the gauge would be on the end-stop, so I guess I do have a connection there somehow, but probably only through the three bolts on the front of the tank, given the rubber bushes around the rear mounting hole. I guess my paint hasn't survived quite as well as I had hoped!

I've seen images of a tank with two spade connectors on the sender plate, where as mine only has one. Is one of those for the earth, or is it (as I think I read somewhere) for a simple 'low' switch? Any idea what colour wire is used for the other connector?

Thanks,
Adam

Blackburn · May 29, 2020

Put an earth wire on one of the sender fixing screws , also worth pulling sender and checking gauge with it out the tank the floats have been known to catch the tank side.

steve2286w · May 29, 2020

Yes the other Lucas terminal would be the low,fuel light if fitted With a green white wire
It should earth through the tank fittings so you may need to clean up one of the bolt fixings
If you Earth the wire it should read full
If you’ve had sender out ensure it’s not hitting the pipe inside

TheMegaMan · May 29, 2020

OK, thanks @Blackburn and @steve2286w. I've not had the float out, but I did remove the pick-up when debugging the fuel pump. Wouldn't hurt to check it, I suppose, although I was hoping not to disturb it if I didn't need to. And yes, makes sense to put a proper earth tab on one of the fixing screws while I'm doing it. I'd rather do that and make sure the sender body is earthed, I think

Cheers!

Gord Wedman · May 30, 2020

If the mechanical voltage regulator was shorted out and feeding 12+ volts to the sender would the guage read high?

Could anyone give me the proper name or part number for those plunger switches and where to buy them? I broke a terminal off one while trying to get our tank guages to work.

By the way I purchased a new Bosch sender from Amazon for around $37 and it seems to work. I did have to swap over the mounting plate as the LR one is non-standard pattern with only 4 mounting holes.

steve2286w · May 30, 2020

If you google the number on the box 510267 Land Rover switch lots places pop up some may Need international post for you

Blackburn · May 30, 2020

@Gord Wedman
The parts you are looking for are in the optional parts catalogues . If you do a web search for Smithies landerover it will bring up a NZ website with some pdf versions site well worth a visit.

Gord Wedman · May 30, 2020

Thank you guys for the info on the change over switch. Found one on eBay in the UK and have purchased. I added a toggle switch to the dash to do the same thing but would like to go back to the original.

TheMegaMan · May 30, 2020

And all sorted with my sender, too. Removed it from the tank as suggested, to find the float arm was just fixed in position. Presumably at the level of fuel at which it sat for about 6 or 7 years before I started the rebuild.

Managed to free it up, took the sender apart and gave it a good clean up inside, and seems to be working perfectly again now. I love the internal design to allow it to compensate for the non-linear angle of the float arm with the level....very neat.

Also added the earth wire, although it looks like it was actually getting a good enough earth before. Should be more rust-tolerant now, though.

Cheers, all!

NjHall · May 31, 2020

Hi all,

I could still do with some guidance before I shell out some cash! I wired each sender up to the gauge individually and found that they both still read 'Full'. So on the passenger side, which is easier to work on, I did some cleaning up and attached a new earth strap as suggested. Even then, out of tank and in tank with float moving it reads 'Full' all the time. Got me wondering whether the earth still wasn't good enough...

After this, I disconnected everything and took the sender apart (As far as I could, any tips on how to get it apart completely would be great). From what i could see, the connections were meeting and have been cleaned up. After refitting, the gauge still reads high...

Does this sound like I need a new sender? I read in Gord Wedman's post above about the voltage regulator potentially being an issue, but not sure which way to go first or how to test that. Sorry for all the questions, but one final one, whats the difference with 24v and 12v senders + how this affects me when buying new haha. I am very new to auto electrics so bear with me!

Thanks again,
Nick

TheMegaMan · May 31, 2020

That looks exactly like I was doing yesterday! I've you've straightened out all three tabs on can, then it should just lift back from the 'back' (the plate the arm goes through. There's a little spring that sits on the end of the arm spindle that connects to the can, so make sure you don't lose that, and the spindle was a little tight in the hole, but mine did just come off. Is the little screw head moving with the can, or is it attached to the end of the spindle? Mine was firmly attached to the spindle, but looking at your photo, I wonder whether it's coming away with the can, rather than staying on the spindle. Try pushing it into the sender body, if it's a tight fit in the can.

Once you've removed the can, you should see the contact wiper on the arm spindle, which moves over a 'coil' of resistance wire. I cleaned mine up with a bit of scotchbrite (along the wires, so as not to distort or break the wire coil), and it all seems well again.

Series 3 Sender unit/ Fuel gauge issues

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