Fuel Gauge

[SteveWood]

Having just about completed a re-wire of my Javelin - started after a near disaster with bare cables in the old loom, the last thing to connect up is the fuel gauge. I have power to the gauge and return from the sender unit but the gauge won't register? Nothing is moving at all. I'm sure it worked before I started. Any suggestions?

[Tony Fearn]

Hello Stephen.
There's quite a number of references to fuel gauges on JowettTalk.
I put this in the pre-war search box and the following came up:-
viewtopic.php?p=22473&hilit=fuel+gauge#p22473
Hope it helps.
Tony,

[SteveWood]

Thanks this is very helpful. I need to know the connections on the back of the gauge - ie which stud is connected to live and which is from sender. They dont have the identification letters given in the wiring diagram. T B

[Keith Clements]

Is it an early or late and a standard gauge?
If you have an ohm meter measure the resistance of each to case.

[SteveWood]

1952 standard I think. Says Jowett on ther middle of the cluster. I will need a little more infor on how to measure the resistance?

[Chris Spencer]

Steve - Before getting really involved in taking things apart and measuring ohms try running a direct earth to the rear of the gauge

[Keith Clements]

The question was which terminal goes to the tank and which goes to the ignition switch. The case of the gauge and the base of the sender unit must be directly connected with zero or less than 1 ohm between them. If you are relying on the chassis to do this there must be no rust or paint or other insulation between the two.
The gauge measures the resistance between its case and its sender terminal by measuring the difference in current going through one of its coils between its ignition terminal and the sender terminal and the other coil between the sender terminal and its case. If the case is not connected to the earth side of the battery then no current will flow through the second coil but may flow through the first coil if the sender unit case is connected to the earth side of the battery and the sender unit potentiometer is varying its resistance as it goes from full to empty.

Thus an ohmeter is useful in checking. The resistance between the ignition terminal and the sender terminal will be about half that between ignition terminal and case with both wires disconnected from the gauge. You can thus identify which terminal is which. You can also measure the resistance between the disconnected wire going to the sender and the case which should vary with different levels of fuel and be comparable to the resistance of one of the gauge coils when tank is empty.

When the tank is full the sender unit should measure about zero ohms and thus shorts out the second coil of the gauge.

If a non standard gauge or sender unit is fitted the gauge may not read correctly but should move.

[SteveWood]

bugger

[SteveWood]

So after putting new batteries in my multimeter and checking the gauge is earthed, plucking up courage to have a go I got the following readings:

Ign to sender = 60
post 1 to cse 156
post 2 to case 97

does this mean post 2 is the ignition connection?

Sorry for being a pain with this but its so frustrating to have completed all the wiring and fallen at the last fence.

[Keith Clements]

No.
The resistance between the ignition terminal and the sender terminal will be about half that between ignition terminal and case with both wires disconnected from the gauge. You can thus identify which terminal is which.

What do you mean by
Ign to sender = 60 ? Are you measuring between the two disconnected wires with the ignition switched off?

You need to measure gauge case to sender wire, gauge case to battery terminal earth as well. All measuerments with wires disconnected from gauge.

You can also measure voltage on sender terminal with just sender wire disconnected which should be about 6v with ignition on and drop when sender wire is connected. This will prove coils in gauge are ok. But the gauge should be moving! If it is not then the pointer maybe stuck.

[SteveWood]

Sorry I followed your directions very carefully - but as it turns out a friend of mine (owner of Priory Motors stopped by today to discuss the work he's about to do on the engine) and he tersted eveythng and both the gauge and the sender are faulty. Sender unit not working at all and guasge in very poor state. Time to get gauge repaired and find a new sender unit for the tank - any suggestions?

[Keith Clements]

The sender unit can be rewired if the coli is broken, but sometimes a clean up with contact cleaner inside will fix .
Gauges too can be repaired. Maybe putting 12v across the sender or down the the sender coil blew the coils.

[Chris Spencer]

Hi Steve - Try the following for the sender unit

https://www.holden.co.uk/search/fuel%20 ... der/page/1?

https://www.holden.co.uk/p/sender_for_s ... p_mounting

https://www.carbuilder.com/uk/fuel-tank ... ole-flange

If all else fails the generic / universal sender from car builder solutions fits but requires the float arm length setting up correctly likewise with the Smiths one from Holden but that is 2 x the price of Car Builder Solutions

I might have a spare Smiths fuel gauge I can send you but I'll have to have a look - I'll forward you a mail / give you a call if I find one

[Chris Spencer]

Steve - Apologies what I thought was a 3 gauge standard Javelin instrument wasn't - turns out that its a speedo head - I'd try JCS to see if they have anything