Odd fuel gauge behaviour - 24v

Ever since I bought my Series 3 the fuel gauge has never worked - the needle always stayed at the bottom of the gauge. During the enforced rebuild at the end of last year I took the opportunity to overhaul the fuel system by sealing the tanks and replacing the senders, filters, tap switches etc.

When at last she was powered up again I was surprised/annoyed to find the gauge still did not not move - closer inspection revealed that when the ignition was turned on the needle flicks downward momentarily but that is all.

I've tried directly earthing the sender to the chassis rather than relying on the securing screws - no change. I tried by-passing the changeover switch connecting the gauge direct to the sender - no change. A multi-meter confirms there is continuity from the tab to the sender unit and that there is +24v going into the gauge.

This is a very early series 3 that had the capillary oil and water temp gauge's so the power feed is a bit different to later models. Looking on the back of the fuel gauge there is a single tab at the top of the gauge to which the +24v feed attaches to and a double tab at the bottom that has one of them connected to the sender.
What I do not seem to have is an earth on the fuel gauge.

So - I guess the questions are - should the second tab be earthed to one of the thumb screws.???

Or is the fuel gauge likely to be stuffed and need replacing???
Having had a 24v feed short a couple of times I' wary of hooking an earth up in case it happens again.....

I'd be interested in peoples thoughts please.

I've no experience of 24v stuff but I would have expected the gauge to be fed from a voltage stabiliser and therefore be fed with less than 24v - the wiring diagram shows one too. On the 12v systems the stabiliser is mounted on the back of the clocks behind the dash. Could this be your problem?

oxides said:

I've no experience of 24v stuff but I would have expected the gauge to be fed from a voltage stabiliser and therefore be fed with less than 24v - the wiring diagram shows one too. On the 12v systems the stabiliser is mounted on the back of the clocks behind the dash. Could this be your problem?

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There is no stabilizer on the 24v systems, at least not on ex-Mil systems. The wiring diagram does not show one, but does show an earth on the guage - but whether that is an earth trough the gauge itself or needing the separate earth is open to question. The other two gauge are capillary so the only electrical feed is the panel lights - and ISTR they have a separate earth from the bulb holder.

Thanks for the suggestion though.

55FM58 said:

There is no stabilizer on the 24v systems, at least not on ex-Mil systems. The wiring diagram does not show one, but does show an earth on the guage - but whether that is an earth trough the gauge itself or needing the separate earth is open to question. The other two gauge are capillary so the only electrical feed is the panel lights - and ISTR they have a separate earth from the bulb holder.

Thanks for the suggestion though.

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OK - the only wiring diagrams for the S3 24v vehicles that I've seen have a stabiliser on them. The earth on my 12v series is through the sender mounting screws to the tank. Can't think of anything else to suggest.

Confused me at first too - esp. as the wiring diagram for a Lightweight does show a stabiliser!

But if you look here: http://www.lrfaq.org/Series/images/lfig148.gif

Item 48 is the fuel gauge and there is only a Light Green wire coming off fuse box terminal 8 supplying the +24v feed to the gauge.
Then a Green/Brown feed from the gauge down to the change-over switch, item 55.
From there it is split into the Left (Green/Purple) and Right (Light Green/Red) feeds to the tank senders, items 68 and 69, which - as you say - are earthed.

Found a diagram for the FC FFR which should have similar electrics and you're right - there's no stabiliser. I assume the gauge is a hot wire type and connecting it up the "wrong" way won't make a difference. Looks like the gauge might be buggered.

oxides said:

Found a diagram for the FC FFR which should have similar electrics and you're right - there's no stabiliser. I assume the gauge is a hot wire type and connecting it up the "wrong" way won't make a difference. Looks like the gauge might be buggered.

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Yeah - I am thinking it might be this too! Thanks for confirming it
Now murphys law kicks in - when I didn't want one there were loads up on eBay - now I am looking they are scarcer than rocking horse droppings!!