Fuel gauge sender

[Swanrad2]

Spent the day fitting a fuel gauge sender in my fuel tank, suspect it works on a variable resistor actuated through a raising and lowering float. I don't know much about electronics - but am learning, slowly so if my explanations are poor I apologise. A positive and negative is wired into the gauge itself with a single wire from the sensor to the gauge (plus a positive for the light). On connecting to 12v power (leisure battery), the needle deflects to 'full' on the gauge. Disconnect the gauge, the needle stays on 'full'. I suspect a faulty sender - how do I test this theory? The instructions with the unit are fairly basic but there doesn't appear to be a calibration control.

Sorry if this is basic, but it is a first step on the road to electrical competence.

 

[West Coast]

Hi - understand the 12v supply is applied to the gauge, but there must be 2 wires from the sender to the gauge, to make a circuit ?

 

[nigelmercier]

Did you check you had the right type of sender? There are two basic types: low R on full, or high R on full.
Does the needle move when you move the float?
[Later] As above: you also need a battery negative. While this can be taken from a common point, it is better to run another lead. The negative terminal may be marked with an earth symbol:

 

[obmij]

Have you connected to earth? Quite easy to test just connect one wire to the positive on your leisure battery and the other to something presumably grounded i.e other earths. When testing this I just touch the negative wire to the top of the alternator as it's unpainted and at the front of the engine.

I had the same problem with a temp sensor gauge always reading max - it turned our no connection to earth. Made the connection - all sorted!

 

[obmij]

BTW I found this book very useful when getting to grips with the mysteries of wiring

http://tinyurl.com/o83jq4o

 

[Swanrad2]

Have you connected to earth? Quite easy to test just connect one wire to the positive on your leisure battery and the other to something presumably grounded i.e other earths. When testing this I just touch the negative wire to the top of the alternator as it's unpainted and at the front of the engine.

I had the same problem with a temp sensor gauge always reading max - it turned our no connection to earth. Made the connection - all sorted!

In the wiring diagram is a large picture (same as that two Posts earlier) which is, obviously, to earth - I am a muppet. Sorry and thanks!
Learning can be a painful experience...

 

[Robert Wilson]

BTW I found this book very useful when getting to grips with the mysteries of wiring

http://tinyurl.com/o83jq4o

Thanks for that. I very much like the look and approach taken in that book. And I appreciated the Amazon facility to "look inside" the book to see if worth buying (well done Amazon).
I shall be buying the book.

I hope Mr Pat Manley isn't related to the Manley who sailed the Atlantic in a Mirror-sized boat in the 60s? I certainly don't want a risk-taker instructing me on my boat electrics :nightmare:

 

[nigelmercier]

BTW I found this book very useful when getting to grips with the mysteries of wiring ...

If you can wait a couple of months there is a new edition coming out:
Essential Boat Electrics [Paperback] Pat Manley
http://www.amazon.co.uk/exec/obidos/ASIN/1909911100/dolcetto-21

And then of course there is Calder's bible:
Boatowner's Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems
http://www.amazon.co.uk/exec/obidos/ASIN/0713672269/dolcetto-21

 

[Swanrad2]

If you can wait a couple of months there is a new edition coming out:
Essential Boat Electrics [Paperback] Pat Manley
http://www.amazon.co.uk/exec/obidos/ASIN/1909911100/dolcetto-21

And then of course there is Calder's bible:
Boatowner's Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems
http://www.amazon.co.uk/exec/obidos/ASIN/0713672269/dolcetto-21

I will be treating myself to the book when the new edition comes out - looks good. Thanks.

 

[Robert Wilson]

Thanks Nigel. Good information - shall wait.

RW