[Shotimes] semi OT: how do senders work?

[Justin Schick]

Hi all,

I'm hoping some of the more knowledgeable listers will be able to
answer a question for me. It has to do with my Mustang project, but
could easily apply to the SHO:

How do one-wire pressure or temp senders work?

I was wiring up the relay (Painless) for my fuel pump on the Mustang,
and remember reading / hearing that the best way is to run the wire for
the switched power source to the sender for the oil pressure gauge. This
way, the fuel pump only switches on when there is oil pressure, which is
a better scenario than having it constantly running as soon as the key
is turned past off. I wired it up like this and then began to wonder if
it'd actually work. Is the sender sending voltage to the gauge (meaning,
it'd work for my fuel pump relay), or is it grounding itself (meaning
I'd need another signal source for my relay)? Inquiring minds want to
know! Thanks in advance,

Justin
silver 92 SHO in KC MO, along with a couple other Fords