Petrol gauge sender

[MickG]

Meg wrote

Mick, Jimj has a negative earth car so won't be using a stabiliser and your sender is the wrong type. I know it doesn't work because I had to replace it with my old sender when I bought a new tank.

Sorry to disapoint but my Sprint is also a negative earth and I have a voltage stabiliser ( the thingy that fits up behind the dash) fitted and always has been. Also my petrol gauge works fine
Regards Mick G

[MickG]

Jim

With the ignition on what voltage do you get on the green wire from the voltage stabiliser to the gauge?
If in doubt check the workshop wiring diagram.

The tank sender is earthed using the black wire connected to the spade connecter on the metal part of the sender unit. Not the insulated terminal. The tank will be earthed when you fit the sender by the screws used to secure it.

Mick G

[Quart Meg Miles]

Meg wrote

Mick, Jimj has a negative earth car so won't be using a stabiliser and your sender is the wrong type. I know it doesn't work because I had to replace it with my old sender when I bought a new tank.

Sorry to disapoint but my Sprint is also a negative earth and I have a voltage stabiliser ( the thingy that fits up behind the dash) fitted and always has been. Also my petrol gauge works fine
Regards Mick G

Shucks, I've mentally done a double inversion of polarity on Jim's car and talked about the wrong type of gauge! It's the early positive earth type that uses the double coil magnetic vector gauge while the later negative earth alternator-regulator cars use a hot wire gauge. Unless, of course, Jim has a negative earth dynamo conversion? I do apologise and will edit my earlier submissions.

Usually the tank body isn't earthed as it attaches to the fibreglass body so it shouldn't matter if it connects to the sender or not. But perhaps it has been earthed for RF suppression or reduced spark risk.

Jim, Could you confirm which type of electrical system you have: dynamo (configured negative earth) or alternator with a regulator for the instruments. The latter gauges are usually very slow moving whereas the early types are pretty frisky. As I edited into an earlier post, my early fuel gauge reads beyond Full when a lead is disconnected from the tank which sounds like your system.

[billwill]

During a conversion from +Earth to -Earth or Dynamo to Alternator, one wouldn't necessarily change the fuel gauge system.

The two-coil gauge is not, I think, polarity sensitive, because it just works by attracting a soft-iron chunk on the needle pivot. It is possible that this is not sensitive to supply voltage and so might not need a voltage stabalizer.

The thermal bi-metal one is certainly not polarity sensitive as it just works by the heat of the wire. This one is however sensitive to supply voltage and does need a voltage stabalizer. But that stabalizer need only be the pulsed average-voltage type as used in my Elan. {it is a contact that switches the supply off & on to maintain an AVERAGE voltage that is stabalized}.

[jimj]

Thanks for all your comments, some I could actually understand. Today I took out the tank, tested again the old sender in my hand which worked fine, installed it and it still worked. I`ve put the tank back in and it still works. All I can guess is that 1 of the 2 terminals is insulated and maybe the insulation was faulty.
Jim

[davidj]

Further the posts about the different Elan petrol gauges, sender units and impedance I thought I would post what I have discovered during my S3 restoration.

Firstly, the gauge and sender is different on the S3 and I guess the earlier models compared with the later versions of the car. The needle is the full length of the gauge unlike the later type (which was also used on the triumph dolomite etc) My sender unit was shot, and I could not find an earlier version to match the gauge, while the later ones are widely available at around £50.

However, I stumbled across a picture of an MGA petrol gauge, which looks the same as the early elan one, but badged as a Jaeger. (I think Smiths owned British Jaeger) The good news is that MGA sender units are available for £15, including gasket and screws, be it M5, on ebay.

I took a chance and purchased the sender unit. It worked! I have not yet filled the tank with petrol, but moving the arm alters the position of the gauge from empty to full.

Few points to note.

The fixing hole pattern is slightly different. However the unit works at a slight angle so I twisted the arm so the float is horizontal when fitted.
There is no earth tab so I fitted one onto one of the fixing screws.
The arm length is shorter than the Elan one, but still moves full arc in the Elan tank
The gauge also has earthed to work and functions with positive or negative earth.
The ohm range of the sender measured 5 - 85 on my cheapy multimeter.

[Quart Meg Miles]

That's worth knowing, David, though my petrol gauge is one of the few instruments still working correctly on my car!

BTW do you still have your red +2?

[davidj]

Yep, still have the +2 and the Sylva Stylus. What I don't have is garage space! (first world problems......)