Oil pressure sending unit

[Basher]

I have a problem with my 1983 Wagoneer, the oil pressure gauge reeds zero. When I´m looking att the sending unit I see two units down there, one with one conection and the other has two connections, they look like these:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1858873327

The one with two connections are not connected. When I look in the Haynes manual there is only one unit so can anyone explain what the two units does. Thanks.

[Kris]

The larger one with the single wire is the pressure sender for the gauge.
The other with two wires is a pressure switch that i believe is for the idiot light.

kris.

[Basher]

And what is the idiot light???

[Al Johnson]

I read someplace, darned if I remember where, that the 2-wire switch is used for the electric choke circuit. That way, the electric choke doesn't begin to open until the engine has actually started and has at least a tiny bit of oil pressure. This might not be right in every case, but it's worth looking into if, say, you were planning on getting rid of the switch or using it for something else.

HTH
Al

[Bob Barry]

Yes, the two-wire switch cuts off current to the electric choke so it doesn't heat up and open when the motor's not running. You need to hook that back up, then test the other sender or the wiring to it.

[mdill]

The pressure send one is the one that looks like a bell (big can)
don't take the one that the parts store gives you, open the box
when he gives it to you and explain that you want the one with
the screw stud connector sticking out the top, not the one with
push on button stud. I have no idea why all the parts books seem
to be wrong but every one I have run in to is wrong. The wrong/
right senders are the same in every other way though.

Mike D.

[PhilSine]

Yeah, I got the one with the button type connector and the PO had changed the connector to accomodate it. It works well but the stupid connector slips off if you even look at it the wrong way.