fuel level sensor to triger relay ckt

Hi, I'm looking for a circuit which would trigger a 12V relay from a fuel level sensor so that when the fuel tank is full the relay is triggered. I believe the fuel level sender reads 560 ohms empty and 55 ohms full. That means I would like to trigger the relay at or below 65 ohms but not higher. This is for a '87 Vanagon and I want to disable a pump transferring fuel from my axillary tank to my main tank when my main tank is full. Thanks for any help, David

Thanks IAAI, Yes, I will build it as it looks pretty simple. Is that an op-amp there in the middle? Like a 741 or something? What part number would you suggest for that? And any help with the transistor part number would be much appreciated as well. Thanks! David

That's a low-level circuit but just invert the inputs. Similar circuits should with most OpAmps (split supply) else single-supply & Comparators etc. It's really just a voltage sensing/comparison circuit with a capacitor as an input "slushing" filter. It's easier if you can find the voltage of the sender/gauge near full (probably between 0-1V, empty should be higher). Because it's near 0V when full, maybe just a simple inverting transistor circuit will do (ie, when sender above 0.7V, transistor #1 turns on which turns off transistor #2 & the relay). Usually low-level sensors are sought. For those I like the separate senders which are quite accurate (being position only albeit subject to slushing) and independent of the sender & gauge. I suppose one could be mounted at the top of the tank, and inverted (whether mechanically or electronically depending on the sense method).

Yes that is a 741 op amp.  Each manufacturer will have thier own prefix before the 741, it really does not make a big difference which manufacturer you use for this application.  This transistor should do the job without heating up hardly at all.  http://www.radioshack.com/product/index.jsp?productid=2062611   This is the thread I was looking for a while ago.  Lots more reading that the one I posted earlier.  I do not think you will need any of the added regulation for your need.  https://www.the12volt.com/installbay/forum_posts.asp~TID~110766~KW~low+fuel~PN~0~TPN~1  In the above link, both of the circuits use 2 fixed resistors instead of the pot in yours.  If you are going to use one of the regulator circuits and can give me a voltage that you want the device to turn on at, I can figure out the values and you can use the fixed resistors.