Fuel gayge conundrum

[guystrungout]

Hello, I read the correspondent from South Africas' fuel gauge problem with interest hoping that it might go some way to helping me solve mine, but sadly not. My problem is far more confusing.... I have a '55 Moggy with a gold faced speedo and have replaced both the tank unit and the fuel gauge as neither were working when I got the car. The tank unit does work now but strangely it seems to work backwards, showing full when it should show empty and vice versa. Also the gauge works but not unsurprisingly goes to empty when it should be full and works its way up to just over half a tank when empty. Simple enough I thought, I'll just reverse the wires on the back of the fuel gauge..but no! It doesn't work at all when I do this.
There is only one wire on the tank unit, and it isn't live, and when the unit is earthed outside the tank but with this wire still attached the fuel gauge goes to full, as you would expect and is normal for any vehicle. I have tried using a different earth to the tank unit in case the unit wasn't earthing properly through the screws but it made no difference.
So what is going on?
Is my fuel gauge at fault or is it the tank unit? I am totally baffled and would be very grateful if anyone could give me some advice on what I can do about it. PLEASE help me, I'm going mad with frustration!! <br><br>

[Lukey]

Sorry I can't answer your question but I have to ask is that minor in matt black? It looks stunning. Where abouts in mid wales are you? I think I saw you driving in to Betws-y-coed last Sunday?

[guystrungout]

Yes, well, its sort of eggshell really. It was like that when I bought it and I love it too! I live in Llanfyllin, not far from Welshpool/Oswestry area. And sadly it wasn't me you saw, I haven't been out that way in the Mog yet. But I will!!

[Alec]

Hello Guy,

the more common gauges do normally show full if you earth the sender terminal cable, if disconnected with the ignition on it should have about 12 volts on it.
However I believe some older gauges show empty when the sender cable is earthed. If that is so, the it sounds as if your sender and gauge are incompatible, unless you want to read the gauge back to front .

Alec

PS, note my location.

[guystrungout]

Hi there and thanks for the information, you may well be correct in your assumption. I replaced my original 50's tank unit with one from a 66 mog, not thinking that it would be any different. Its 11 years younger which might well mean it workings are different to the first one. They are after all a completely different shape! What a fool eh?
And yes, good to hear from someone not too far away for once..you don't own that lovely white Mog with lots of lights on the front that lives opposite the motorbike showroom on Walls road do you? There don't seem to many Moggy's around this neck of the woods do there? But I have made contact with Jonathon Evans who is in Ford, just up the road from Welshpool and he's pretty handy for tips and bits. Do you know him? If you don't you should!

[rayofleamington]

So what is going on?

The early sender unit reads the other way to later sender units - easiest solution is to get the other type of sender. The change over (I'm led to believe) corresponds to when they stopped using the gold faced speedo mid way through Minor 1000 production.

The later tank is likely to have a bigger volume. The early ~22 litre tank is pretty small by most people's standards.

[guystrungout]

Hi, well yes this does seem to be the problem, which is good because at least it means I know what it is now and can remedy it, provided I can find another early tank unit.
Thanks for your help, its much appreciated.
Forward into the past!

[rayofleamington]

which is good because at least it means I know what it is now and can remedy it, provided I can find another early tank unit.

I'm not sure you want an early tank unit! My comment that you want 'the other type' was a catch all!

From memory your gauge is working like a later one... i.e. when sender wire is to ground guage reads full. Therefore to match it you need a sender that is low resistance when full.

I'm pretty sure that's the later type sender (but you'd need to check) so it should be easier to find - there's still a fair few later Minor 1000's being scrapped.

[guystrungout]

I'm completely confused now!!
I have replaced the fuel gauge with another of the same type (ie Gold faced) that has a pointer that works, the one the car came with had no pointer at all.
And I have replaced the original tank unit (an early type with the raised screw down top) with one I took out of a '66 saloon, with a flat top, mistakenly thinking that it would work fine.
Which it obviously doesn't.
I hope I'm not appearing to look incredibly stupid here, but surely if the gauge and sender are incompatible, then I need to get one that is, which to my mind should be an earlier type, like the one I originally replaced?
If I replace it with another later sender I will surely end up with the same problem?
Apologies if I am missing something obvious and vital in your advice, I have read it a few times now and am still confused!

[rayofleamington]

Sorry for the confusion - I'm not an expert for fuel senders and am picking things out of my memory. I could be lass vague, but that runs the risk of telling you to do something as fact when it's only a guess.

If it was me I'd re-check the gauge operation. If the gauge reads full when the wire to the sender is grounded*, ask someone with a later car to do the same test. If there's does the same, then I'd say to fit a later sender unit.
* I think that's what you said happens but it's not fully clear.

If the gauge goes empty when you ground the sender wire, then ideally try to get someone with an early car to check their's is the same and if so, get an early sender unit.

[Mogwai]

When switched on does the gauge move instantly or rise slowly. the early ones are a moving coil & will rise/ fall fast & the later type use a bimetalic movment & will rise/fall slowly also this type will need a voltage stabiliser.
sounds like you may need the earlier type sender from your description

[guystrungout]

Thanks chaps, that sounds nice and straight forward..I think I can cope with doing that! Thanks for all your help and advice..what a great service this is to be able to plug into.
Forward into the past!