Oil pressure sending unit question

My 82 D250 has 2 oil pressure sending units in the back of the motor, one is the standard sender for the gauge....The 2nd one is the one I have questions about....It has 3 prongs and I wonder what it does? I cant find it in any wiring diagrams. I'm wondering if it has any relation to the fact that it wont run in the run position since the engine swap...It only is getting fire while cranking....I know this is a classic ballast resistor problem.

Thanks
Rick

Ah looked it up on Advance autos page its a oil light switch.....

http://shop.advanceautoparts.com/p/carquest-by-bwd-oil-pressure-light-switch-s385/5971721-P

Appears I have a light and a gauge....

The 3 prong switch is for controlling 12v power to the heated carb choke thermostat. May also control an oil light if equipped. The 2 terminals across from each other should have continuity when there is oil pressure. These will go to the choke thermostat. The other terminal will ground without oil pressure present. This will go to an oil light. The bell shaped one wire sender controls the gauge.

Thanks good info