[Junket]

Rob What I would do is hook the ohm meter (digital works best) to the sending unit move it threw the cycle see what kind of reading you get I belive the SW guage read ohm between 33-240 or 270 the senders should be pre 89 fords run 73-12 ohm 87 up fords are 10-180 ohm. Most inportant is the ground hook it to the tank unit it self (tank unit should have a gasket under and will not get the correct reading) I don't know about the SW guages but on the GM no ground or dead ground that does to the read side of the guage will cause a full reading.
Hope it been a little help.
Ken