Fuel gauge

[olonas]

I've just filled up my Traveller with petrol and the fuel gauge only indicates 3/4 tank.
Earlier in the week when I filled up it indicated full. It was showing 1/2 tank when topped up this time but I think there was more in the tank, it only need about 12 litre to brim.
It is the black speedo head with voltage stabiliser and slow rising fuel gauge.
One clue though, and a bit of a coincidence I had to renew the high beam warning lamp since last filling up, I didn't disconnect battery (very naughty I know) when doing so. I did touch the dash a couple of times with electrical bits, possibly with the fuel gauge and there was sparking.
Any ideas please? Could I have damaged the gauge and/or the voltage stabiliser? Or something else?

[Willie]

Quite possibly....if you feel for the sender unit on top of the
fuel tank you will feel a Lucar push-on connector, if you remove
this and short the connector to the chassis the fuel gauge should
read 'full' (with ignition on). If it does not then it would seem that
you have damaged the voltage stabilizer and/or the gauge.
it is more likely to be the stabilizer. If you have a meter you can
check the stabilizer voltage which should be 10volts
(You check for the 10volts between the Light Green wire on the
stabilizer and chassis).....................Willie

[olonas]

Thanks Willie, I'll follow your advice tomorrow morning and advise result(s). Probably self inflicted this one It just goes to show that best policy is to disconnect battery earth when working on the electrics.
There was also a strange happening when I'd replaced the speedo. When the sidelights were switched on the speedo illumination went out and the high beam warning light came on! Switched on head lights dipped and main, panel lamps on and high beam warning off??? After a few switchings all was well and has been o.k. since. What do you make of that

[newagetraveller]

The warning lights, fuel gauge etc. are all earthed by contact between speedo and chassis. This takes place at the two sides of the speedo where it is secured by phillips head screws which you access through holes in the sides of the glove compartment. If these screws are not tightened then earthing may be dodgey giving rise to the faults you have described.

[Willie]

Another good one... I think that there was a bad earth to
the panel lights(see Newages posting )so the lamps were
just about working,but when the side lights were turned on
they had better earth points which meant that the volts took
this easier path to ground and in doing so extinguished the
panel lights(the side lights and panel lights are fed from one
common point. You will often see this on a car in front of you
when the stop lights are on and the indicator is then turned on
and both the stop light and the winker dim down and flash
together. This is the result of a poor earth.
Willie

[olonas]

Checked voltage between stabiliser and chassis with digital multimeter. NOT VERY STABLE! in fact no steady reading at all. This has to be a rather large clue as to what I've destroyed. I'll get hold of a good unit and try that.

[olonas]

Fitted "used but good" voltage stabiliser, now showing a full tank, yes it is full. Hope the gauge doesn't stay in that position!
Re the panel lamps phenomenon - yes it was/is an earthing problem. Tried the same thing after renewing stabiliser with speedo held away from dash. Same thing happened, with speedo in position is o.k. The vehicle is a '57 Traveller but fitted with all post '62 equipment from a donor vehicle. Speedo is therefore not as original bronze face. The present unit is secured into dash aperture using split surround and a small self tapping screw (not noticeable) at the bottom. I was advised when the car was purchased that this has to be done because the black speedo will not locate with the original brackets on either side and there is a difference between the securing bracket positions for the bronze and black speedo's. Does anyone know if this is the case as I would prefer to use the correct screws? The unit is secure enough but the method of fixing could possibly cause the problem indicated with the panel/high beam lamps.

[Willie]

My 1957 convertible is also fitted with total 1098 running
gear including the black speedo, it is held in position by
the normal screws. The only problem I am aware of when
swopping to a 'black'speedo is that the fuel gauge will not
work unless you also fit the later tank sender unit. Glad you
identified the problem and good to get some feed-back
Willie

[olonas]

Thanks Willie. I've got a couple of spare securing screws, the speedo isn't back in place yet. I'll try refitting using correct screws, hopefully they'll line up with brackets and, when tightened, improve earthing.
I thought it strange, and didn't enquire further, when told that black speedo will not fit in earlier cars. It would seem a needless excercise for a car maker to change something like that, surely they would, and probably did, just tell Smiths to make black speedo to previous fitting arrangement sizes.

[olonas]

Yes, the correct mounting arrangement lines up and works o.k. Can't think why previous owner thought this would't be suitable.
And yes the fuel gauge needle is moving from full
Thanks for assistance Willie.