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MG Midget and Sprite Technical - Fuel Gauge problem

I can't get my gauge to work properly and therefore am requesting some help/clarification if possible.


I have a 10v supply from the LGG wire - does this attach to the Empty side of the gauge or the full.
When on the empty side - the needle does not move, if I attach it top the full side it reads full.

At the tank I have a brand new tank and sender - the tank is in situ. with 2 wires from the sender - (these were added when I bolted the tank up - this allowed me to wire it up when the loom was in place weeks later -

it doesn't matter which combination of wire connections I make I still get no reading on the gauge?

Any ideas?? Faulty sender - a short in the wiring between the gauge and the sender???

Many Thanks
JOn
Jon White

Hi Jon,

LGG to F side of gauge

GB wire (from sender) to E side of gauge

check sender is fully earthed

checked gauge is fully earthed

check wires and bullet connectors are clean, secure and protected

also, if you want to, putting your car profile up would help and save asking which model each time
N Atkins

At the risk of stating the obvious...

If the fuel tank is empty won't it read zero on the gauge when you wire it up...? You need to fill it up/wiggle the sender to check it works?

Malcolm
Malcolm Le Chevalier

Malcolm,
I'm glad you put that as I was about thinking it but as I often told my posts are rude or zealous I left it out (and forgot as I went out to check which side of the gauge the LGG wire goes to)
N Atkins

The gauge only needs to have a good earth for the illumination, not the function of the gauge.

I will try and add something more helpful later when I'm not using a tiny Blackberry keypad!
Dave O'Neill 2

in case Jon thinks I am rude, I don't think it is the tank being empty

good point Dave as always

sender needs earth and connections checking though
N Atkins

As it reads full if wired according to Nigel (I assume from what you say Nigel that you have checked yours) it would suggest that either the sender or the wiring is earthing out somewhere. I would run a seperate wire from the gauge to the sender and see what happens.

Trev
T Mason

I agree with you Trev but it doesn't hurt to check the other stuff too obviously not related to this problem but so quick and easy you might as well whilst it is quick and easy to do plus going straight to the answer is less memorable for learning purposes

not that I suggested earth to gauge for that reason, that was more simple, I didn't think it through just typed it all out for speed

you I did stick my head up under the dash to see which way round the wires went, doesn't it always go dark just when you need the light
N Atkins

I thought it does not matter which way round the wires attach to the gauge as all that matters is that a current passes through the gauge which then measures the resistance (the sender unit varying the resistance - or have I got that totally wrong?
Chris H (1970 Midget 1275)

Chris,
I'm not sure, Dave will confirm, this type of information I'm just not able to retain

you do need the votlage stabilizer and Joh has said he has 10v so that shoud be OK
N Atkins

Yes the sender varies the current flow by varying the resistance, (rheostat), but the gauge is polarity conscious I believe.
Lawrence Slater

Or maybe not, if it is bimetallic operation. I have to confess, I never had to find out, so it may be. In which case it shouldn't matter which way you wire the gauge as far as the sender signal goes.
Lawrence Slater

There is some useful info on fuel gauge fault finding on Paul Hunt's website.

Although it essentially deals with MGBs, the principles are basicly the same.

http://www.mgb-stuff.org.uk/electricstext1.htm#gauges
Dave O'Neill 2

That's some great advice there many thanks

I'll have a look at this with a little more inspiration.

No offence taken!!!

Jon
Jon White

Here you go, I found my spare fuel gauge.

You can see the terminals are marked B and T. My guess would be that B is from the fuse box (live only when ignition is on), and T is from the Tank sender. So in that sense it is polarity conscious. Current will flow according to the level of fuel in the tank.

Lawrence Slater

Just been looking at my wiring diagram.

As you have an LGG (light green and green) wire, then you have the later car that includes a bi-metalic voltage stablizer.

So that will connect to the appropriate side of the gauge. If your gauge has the same markings as my earlier guage I would connect that to the "B".

The wire going away from the gauge ( to the sender unit in the tank), should be GB(green/brown). This connects to the "T" side of the gauge.

What colour are the 2 wires on your sender unit?

Hopefully one is GB, and the other perhaps black, which will be ground. (earth).


Lawrence Slater

Lawrence,
subject to Jon having same model car as me we've covered connections and in the same way I made a mistake by including earth to gauge you made a little mistake - GB is green/black, brown is N, black is to earth
N Atkins

Yep Nigel slip of the keyboard and mind GB is indeed black. :)

And as I said, black is to ground.

Nigel my spare fuel gauge is an earlier one, do you know if yours has the same T B markings?

I ask because you said the connections were to the F and E side of the gauge.

By that I assume you meant Empty and Full. Is that how your gauge connections are marked on the rear?

Lawrence Slater

There I go again, I mean GB is Green/Black.
Lawrence Slater

Hi Lawrence,
I followed Jon lead with empty and full side of the gauge meaning from the face rather than the rear

just by looking up from under the dash I'm not able to see any markings on the back probably because the connecting posts on my dial come off those two nuts as it doesn't have have that external cross bar like your earlier dial

I will say that my fuel gauge is two years old and is accurate so I have no excuse for running out of fuel
N Atkins

Hi Nigel,

I tried to look behind my dash too, but there's just no room to see.

I think out of interest, I'm going to pull my spare gauge apart and take a look see. Also I'm going to wire it up, makeshift style, for experimental porpoises. :).

To be honest, I don't even know if it works anyway, or where or when I got it. So it will be a useful waste of time. lol.
Lawrence Slater

This thread was discussed between 19/10/2011 and 21/10/2011

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