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2-wire fuel tank sender?


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Having lost the will to live after reading countless posts on the subject (both here and elsewhere), I have a question - my 200Tdi 110 is fitted with a 2-wire fuel tank sender (there is no 3rd terminal). After buzzing them through with a metre, I realised that they were both for fuel level, and not separate 'low fuel' / 'fuel level' (and neither goes to earth).

When one side is wired to earth, the other provides the connection to the fuel gauge, which then works perfectly. So - does this mean that I don't have the facility to have a low fuel light (Td5 dash fitted)?

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Earth is the ridged stud not one of the spade terminals, 

This my spare tank unit & its notes, part number PRC8463, 

The unit without low fuel warning is PRC8707

 

For the low fuel light to work you need the 3 terminal as below, some 300tdi never had the low fuel level connection on the sender unit. 

 

IMG_20221109_113732.jpg

 

IMG_20221109_113605.jpg

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3 hours ago, Retroanaconda said:

On a td5 dash the low fuel light is driven by a circuit in the speedo head, there’s no feed from the sender. I had it running for years on my 200Tdi with only the level wires hooked up to the original tank sender.

How on earth does that work without a connection to the tank?

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3 hours ago, western said:

Sounds like you have a later maybe 300tdi sender, 

My low fuel light is wired direct from the tank sender terminal to the low fuel light on my Td5 instrument pack. I couldn't get it to work through the speedo circuit. 

I can get the light to illuminate on the dash artificially - just haven't got anything to drive it!

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1 hour ago, Paddy_SP said:

How on earth does that work without a connection to the tank?

Sorry I should have been clearer, there is a connection to the tank but only the level and earth wires, nothing for the warning light. The speedo head measures the ‘signal’ from the sender and when it reaches a certain point it turns on the light.

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1 hour ago, Retroanaconda said:

Sorry I should have been clearer, there is a connection to the tank but only the level and earth wires, nothing for the warning light. The speedo head measures the ‘signal’ from the sender and when it reaches a certain point it turns on the light.

Ah, many thanks - got that! :) 

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8 hours ago, cackshifter said:

So  one possible solution  perhaps simpler than attempting to change the sender and add a wire(I haven't tried this so I cannot say it definitely works) is to use a Spiyda module, see linky

Many thanks - I only just got a chance to sit down and check it out; it looks good, but I'm not sure I want a low-level light that badly!

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