I need to built a circuit that uses a 12VDC relay to control a 12VDC pump. A relay is being used because the pump is close to the power source but some distance from the control point, and the relay saves long heavy cables ($$$).

The pump is usually controlled by a level switch, but on occasion I need to bypass this and force it to run.

Is it possible to set-up the relay like this: -

The pump is connected to the Normally Open terminal 
The control signal comes from a single pole double throw switch.
- On1: Connects directly to the signal input on the relay, switching on the pump
- CentreOff:  The relay stays open and the pump doesn't run
- On2: Connects to the signal input on the relay via the level switch, switching on the pump only when the level switch is activated.

I would solder the two signal leads together and have a single lead connected to the signal input terminal.