Why does my distributor have three wires
	
	
		I have a 61 Galaxie Starliner.  This car is new to me and I'm a little confused.  I want to put an aftermarket ignition box and coil on the 390 in the car.  I printed the wiring diagram from the box manufacturer and they have wires for pick up + and pick up - there is three wires coming out of my distributor, why.
Also the distributor has been converted from points to electronic(magnetic). If needed the casting #'s are D6VE which I believe is 1976 Lincoln. Help.