Series 3 Sender unit/ Fuel gauge issues

ExMil109 · May 31, 2020

Nick, if you have the three military gauges:

then they don't need a voltage regulator for the gauges, but the gauge cluster itself needs a good earth connection, otherwise the gauges will all read high. Do the water/oil temp gauges read correctly?
Are you asking about 12V/24V senders because your 109 is the 24 volt version (FFR)? I'm not sure if the 24V system uses the same senders as the 12V system - hopefully someone on here will know for sure...

NjHall · Jun 1, 2020

Thanks Mega, I will give that a try today, I just didn't want to break anything!
(Edit.... Whoops, it was a pig and after ages of persuasion I got the spindle to pop through, followed by the screwdriver I was using to apply pressure. Swiftly snapped one of the contacts inside! Lesson learned)

That is what my gauges look like, Oil temp doesn't move from 'C' at all (Next job on the list), but the water temp gauge works fine. With regards to the voltage I have no idea how to tell the difference! (Rookie as ever). Thanks for all the continued support

ExMil109 · Jun 2, 2020

You'll know if you have the 24 system 'cos you'll have 2 batteries and a hefty alternator on the driver's side of the engine

It's normal for the oil temp to take a while to show anything - it takes me at least 5 miles of steady driving for the oil temp to start moving off 'C'. But if it doesn't move at all, check the wiring to the sender in the sump - it passes quite close to the exhaust and can get melted...
If the water temp gauge is working normally, it may mean that the fuel gauge itself is faulty. You can replace each of the gauges separately, but they are difficult to find and likely to be expensive

- it'd be easier to change the sender first.

NjHall · Jun 2, 2020

Ah! Well there you have it, 12V system it is

I've purchased some new senders so will see if that has the desired effect.

Thanks for the advice on the oil temp gauge, will take a look into that asap!

Cheers,
Nick

NjHall · Jun 5, 2020

New senders arrived (Wahoo)

But the issues continue! When connecting earthed sender to the fuel gauge, with the rod where empty would be, the gauge reads just under 'F'. When pulling the rod up to where full would be, the gauge moves up slightly to 'F'. When returning the rod to where empty would be, the gauge does not fall back and stays at max position till the ignition is switched off... I suppose that means the gauge is having some sort of fault. Any ideas?

Sender in low position

Sender in high position

steve2286w · Jun 5, 2020

Does it sound like the resistance range in ohms between full and empty of the sender is not matched to the gauge

Blackburn · Jun 6, 2020

Try your new sender connected direct to gauge with a new piece of wire maybe an fault on your wire to fuel tank

NjHall · Jun 6, 2020

Do you mean a new wire right through to the gauge? I’m running new wires from the sender to earth and to where the gauge wire normally meets the switches for testing purposes

steve2286w · Jun 6, 2020

Going back to an earlier query there seems a 24v sender available

Blackburn · Jun 6, 2020

Connect a wire direct to dash gauge attach sender out of tank and clip an earth wire on to see if gauge will then work.

NjHall · Jun 6, 2020

Rightio, I’ve hooked up the sender to the gauge out of tank and earthed. As soon as the sender connect to the circuit, the gauge goes right up to full. I have tried this with a number of wires and earths to be sure... it seems that regardless of the configuration, as soon as the gauge finds a connection it reads full

ExMil109 · Jun 6, 2020

I've had plenty of problems with these Smiths military gauges, including an oil temp gauge that read max as soon as it was connected to the sender, regardless of whether the engine was hot or cold. I think these gauges are not as robust as the Jaeger thermal ones, plus they are fussy about being earthed properly, while the Jaeger ones don't need an earth.
If you don't have any luck with connecting direct to the sender, you could check that the gauges are not corroded internally. There's an earth connection on each gauge that corrodes and doesn't make good contact with the housing. Without a good earth connection, the gauge will read high.

It's a fiddly job to dismantle and clean the gauge contacts, but these are getting rare now and difficult to find (especially as 12V, most of the ones on eBay are 24V).

NjHall · Jun 11, 2020

Hi all,

Thanks again for the fantastic help you have all been so far... Time for a further installation of the Fuel gauge saga!

I have now dismantled the instruments and given them a good clean, although the inside was actually in great condition. In addition, I have cleaned all contacts which meet the gauges and instrument housing etc.

These are now a shining example of electrical cleanliness! Having put it all back together, the problem is exactly the same as before *Feeling exasperated*

So my next thoughts are that I need to chase and clean the 4 cables coming from the threads on either side of the housing which I assume are earth straps. (The nearest 2 loose earth straps on the photo were properly tightened before testing by the way!) Does that sound right? Or could it just be requiring a new fuel gauge now?

Cheers,
Nick

Dippypud · Jun 11, 2020

NjHall said:
Hi all,

Thanks again for the fantastic help you have all been so far... Time for a further installation of the Fuel gauge saga!

I have now dismantled the instruments and given them a good clean, although the inside was actually in great condition. In addition, I have cleaned all contacts which meet the gauges and instrument housing etc.
View attachment 211964
View attachment 211965
View attachment 211966

These are now a shining example of electrical cleanliness! Having put it all back together, the problem is exactly the same as before *Feeling exasperated*

View attachment 211967

So my next thoughts are that I need to chase and clean the 4 cables coming from the threads on either side of the housing which I assume are earth straps. (The nearest 2 loose earth straps on the photo were properly tightened before testing by the way!) Does that sound right? Or could it just be requiring a new fuel gauge now?

Cheers,
Nick

You can check the feeds / earths with a bulb ...

ExMil109 · Jun 14, 2020

Nick, those gauges look in better condition than mine! But they are fragile things in my experience - they use coils of fine wire that seems to break or become disconnected from the terminals. I've attempted to repair one, but they are not designed to be dismantled - I guess an instrument specialist like Richfields would have the skills/tools to do this.
It's always worth checking the earth connections on the cluster (and on the speedo) but you might need a new gauge. The military Smiths gauges occasionally surface on eBay (but often 24V) or a military specialist might have one (at a price!). You could downgrade to the Jaeger 2-gauge cluster in the meantime - these are easier to find and work with the same senders, but they do need the voltage stabiliser on the back of the speedo.

NjHall · Jun 17, 2020

Grand, I’m just In the process of removing the Dash to try and find where the earth goes. After that I’ll send it off.

In the mean time I have some more questions! Does anyone know where I can get another one of these brackets? (Below) One is missing from the Speedo, meaning that all 3 connections to the Speedo via this method are all on one side, rather than split over the two.

Secondly, the earth strap continues to run to this point in the dash. What are these for?

And lastly I’ve been looking into the oil temp gauge issue. Does anyone know where it connects to the sump, as I can’t seem to see one anywhere and wonder if it has rotted off... Also any wiring diagram including this mental military gauge cluster would be fantastic.

Thanks again and hope to move on from this problem soon!

ExMil109 · Jun 17, 2020

NjHall said:
the earth strap continues to run to this point in the dash. What are these for?

These are to connect an inspection lamp (or a battery trickle charger), assuming you can find a plug that fits. They're directly connected to the battery (sometimes via a fuse on the military Landies).
The oil temp gauge reads from a sender in the sump, on the opposite side to the drain plug. You should find a hose from the oil cooler (in front of the radiator) going to the sump; the sender is just next to that hose.

NjHall · Jun 19, 2020

ExMil109 said:
These are to connect an inspection lamp (or a battery trickle charger), assuming you can find a plug that fits. They're directly connected to the battery (sometimes via a fuse on the military Landies).
The oil temp gauge reads from a sender in the sump, on the opposite side to the drain plug. You should find a hose from the oil cooler (in front of the radiator) going to the sump; the sender is just next to that hose.
View attachment 212479

Very interesting! Thanks for the insight ExMil. As it turns out, my Oil Temp Gauge reads 0 Because it has been disconnected. Looks like a new sump has been fitted in the past that doesn't support a thermostat... At least that's 1 mystery solved.

Anyway back onto the Fuel Gauge issue. So I've traced the earth strap to this point, where it runs into, and then out of this box onto the metalwork. Could there be an issue with this here box? The plug and all earths are now clean as a whistle and the issue persists.

If it's unlikely there is an issue here, then i'll send the gauge off to Richfields

ExMil109 · Jun 20, 2020

NjHall said:
Could there be an issue with this here box?

That there box is the flasher unit and the earth connection looks ok. So as long as the indicators/hazards are working I'd say it's ok.
It's quite likely that over the years your Landy has had one or more replacement engines, so the lack of military sump is not too surprising. You might find a military sump turn up, or you might find a spin-on oil filter adapter, which has a threaded part where you can fit a temp sender. Some people don't like the spin-on adapter as it's not original, other people prefer them to the paper filter...
Incidentally, there's a 12V fuel gauge on eBay:

https://www.ebay.co.uk/itm/Genuine-...407534?hash=item3da57c8a2e:g:GXQAAOSw-Nle7U3g

NjHall · Jun 20, 2020

Thanks for the link, the vendor is guaranteeing that the part is fully operational, so I've bought it and will see if it fixes the issue! I also happen to have then spin on oil filter type anyway, so can start to look into that. More news to fllow!

Series 3 Sender unit/ Fuel gauge issues

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