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Hi everyone,

I just bought this 1981 Saab C900 and it has a problem with the fuel gauge always showing up as full. I've been searching what could cause this and I've narrowed it down to what seems to be the fuel sender. The problem is, the fuel sender is disconnected and I don't which cable goes on which of the 4 pin.




I'm guessing the black cable is the ground, the grey and the brown cables are the signal and the warning light and there is the grey/red cable taped to a beige cable going towards the fuel pump.


I have been googling a lot today to try to find my answer but I haven't seen anyone with a sender looking like this one. Anyone here know which cables goes where ? Thank you.
 

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I reckon the fuel sender has fallen apart in the tank (usual) The wiring is shown in the diagram in the manual electrical section in the stickies. If push comes to shove find another 900 and look at that. It's not difficult to work out if you know what you are doing.
 

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My 81 turbo sedan has the original white plastic sender. The signal output is 'reversed' to the later metal can senders apparently. Yes if the sender isn't working (or it's not connected) the gauge shows full, unlike on later build (1983 onward?) where the metal can style came into use.


Note the other big problem with these white plastic senders... Because the fuel pump power is jumped off the top of the sender (instead being fully seperate thick wires like with the metal can sender config), the earth lugs have a tendency to develop poor connections over time and the lugs will heat up due to increased current resistance.



A lot of the white plastic senders have darkened plastic around the earth lug due to long term heating. It's good practise to check all the spade connectors on the wiring and 'tighten then up' so they grip the lugs on top of the sender body better.
 
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