Can anyone please give me some advice on problems I am having with a fuel sender?
The instrument gets 12v across the +ve and -ve, but nothing back on the sender side which I believe should be about 5v.
The tank is about 50% full or empty depending on how you look at these things!
I have taken some resistance measurements and I don't know what I should be expecting to see from a healthy sender.
Resistance readings with the unit on the bench:
+ve to -ve = 1.6 meg ohms
+ve to sender = 1.6 meg ohms
-ve to sender = 41 k ohms
-ve to the outside of the tube = 0 ohms, continuity.
I don't get a reading between any of the 3 terminals and the small inner section of the tube whether the unit is submerged in the tank or not. I'm guessing the level in the tank is meant to change the resistance between the inner and outer tube sections.
Would I be correct in assuming that there is a break between the small inner section of tubing and one of the terminals - probably the sender terminal?
Lots of fuel and level sensors work kind of like this. The switches in the circuit a magnetically activated "reed switches". They are in a tube with a ring shaped float outside with a magnet in it which goes down into the tank. At the float rises or falls it closes or opens the reed switches which in turn changes which resistors are connected to the output. Without guaranteeing it, if you connect 12V onto your sensors 12V and 0V terminals, then run a strong magnet (or the float) up and down the length of the tube and you get nothing on the output the sensor might be dead. If it is this type the reed switches are machanical and wear out after a long time.
Select to expand quote
If you can't get the sender problem fixed it is a good spot to fit a dip stick. 
Some info on your centroid "capacitance" style sender. The CGF-12 appears to be made by Centroid.
www.centroidproducts.com/
Your ohms reading shows the problem, "plus" is open.
In some cases it's possible to fix it.
In most cases its wire broken going to plus terminal , imposible to solder,
you can un-wind one turn to have enough length to re attached .
