The sender is right next to the oil filter. A round sender with a single wire. Maybe the wire got knocked off by accident? To check the wiring and gauge, have some one sit in the truck with the ignition on (not running) and then temporarily ground the wire to the engine for a second or so. The gauge needle should jump everytime you ground and release. If your up for making a little mess, take an empty coke bottle, unscrew the sender, disconnect the coil wire (you don't want the engine starting) and hold the coke bottle tight to the block. Have someone crank the engine briefly (be prepared for the engine to move some when the starter engages) and observe oil shooting into the bottle. This won't tell you how much pressure you have but will at least confirm that there is some. Also, if the sea foam loosened some munge and clogged the sender or sender passage, this should clear the passgeway. You could always go buy a cheap mechanical gauge and put it in place of the electric one for test purposes (or just buy a new sender and try it). If you truly had 0 oil pressure, your lifters would be clattering/tapping like crazy.