zip thanks for your help. As you know, the oem sender is no longer available, but all mechanicals are shared with the SLK320, built on the R170 platform. Hard to read but looks like pn A170 562 1017. Next to that, pressure sender A001 118. Full it reads .5 ohms. Empty it shows 197 ohms. The resistance changes smoothly out of the tank. With the sender out of the tank (but hooked up) if I hold the float in the "full" position the gauge reads "full". If I let it swing down to the "empty" position, the gauge reads "3/4". If I unplug the sender, the gauge drops to "empty".