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PetrolGauge repair
June 28, 2014
5:54 pm
Martin Shaw

I am trying to repair a petrol gauge for a ’30s Hornet Special. Can anyone tell me what is the resistance of the sender unit? Also does anyone have details of the wiring between the gauge and the sender unit? The gauge I have only has two terminals and inside there is a main coil across the to terminals and a smaller secondary coil between the terminals that activates the needle. I can simulate the sender unit using a variable resister but the gauge output is erratic at the bottom end of the scale, just where you want it to be accurate. I would be grateful for any help

June 29, 2014
7:28 pm
Graham Button
Forum Posts: 297
Member Since:
January 3, 2013
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Martin , I’m not entirely sure where your problem lies and I’m afraid I wouldn’t have any idea as to the value of the resistance of the sender unit, but the first check that you should make is the instrument its self, the wire to the tank unit is just an earth return so if you disconnect it and then earth it your gauge should then read full. The tank unit is simply a variable resister so are you saying you are getting the same results using your variable resistor as the tank sender unit gives? I think the first check I would make is to remove the sender unit, earth it and then having connected the gauge wire , get someone to sit in the car and watch the gauge while you slowly moving the float back and forth through it’s full range. If there is any wild fluctuation at any point the cause is most likely to be a bad contact between the resister windings and the sweeper normally due to lack of use, cleaning and the application of some WD40 or similar will usually effect a cure. A 12 volt bulb with the wire from earth side connected to the tank unit and tested in the same way will tell you if it’s working correctly in other words a gradual dimming and brightening of the bulb without any flickering. Doing these checks should determine the fault. If it’s the gauge that’s the problem then I would suggest a enlisting the services of a specialist repairer.

June 29, 2014
10:05 pm
Forum Posts: 308
Member Since:
May 8, 2013
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Hi Martin
I am not sure if anyone will be able to help you with the resistance level you are asking for, but I agree with Graham’s suggestions above. If you do decide that you require the services of a specialist, I can recommend someone for you.


July 1, 2014
7:41 pm
Chris Arnold
Forum Posts: 233
Member Since:
January 4, 2013
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Hi Martin.
I noted your request for information requesting information regarding fuel gauges and sender units and it struck a chord. A while ago I was having troubles with my fuel gauge and I downloaded and printed some information but, unfortunately, I forgot to record the website address. I presume you have a Smith’s gauge and, from the information given, I think it is a G33 system rather than the more normal G35 system. The printoffs I have do include values for the resistance of the sender unit but I think you ought to read the whole article before diving in. I don’t think I can attach documents to a forum reply so, if you want me to scan and forward these documents, please contact me. My details are in Wolseley World or I’m sure the webmaster Bob will point you in the right direction.
Chris Arnold

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