you need an ohmeter, one lead on the connection peg, one on the sender frame [no "polarity" involved] - move the float arm and you should read 0 - 30 ohms

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics