im using a dx harness made for mpfi.. just got a si harness with resistor box...can take the dx engine harness out and put in the si..and do i still have to keep the rpm activiation switch... i will be boosting thats why i want the si harness with resistor box

 

91 harness wont plug into a dual point dx or std car harness

i wish it were that simple

you'd need si car and engine harness to do it the way your talking about