That depends on the ECU choice. A 4 pin ECU only requires a 2 terminal (single) ballast but with your 2 terminal harness you can use the 4 terminal ballast if that is what you have but it would look unsightly (plug the 2 female terminals into the .5 ohm side) & you might ohm both sides seperately & depending on your coil choice you might parallel the 2 resistors of a 4 terminal ballast to reduce the final ohm value (my last parallel one was 1.1 ohms). An OE 5 pin ECU requires a 4 terminal ballast/harness. A parts house 4 pin ECU is the same as an OE 4 pinner (as far as connections go/performance my vary) & only needs a 2 terminal ballast & a parts house 5 pin ECU with a dummy (no continuity to anything) 5th pin also only need a 2 terminal ballast but can use a 4 terminal ballast (same as prior, use the .5 ohm side or parallel both sides). Short version: what coil/ECU are you working with? EDIT & ballast?