Fried ECM

The only difference in the circuit / ECM with the dual ballast is that the second ballast resistance feed power into the 5th pin on the ECU. That is no longer used, and unless you find a really old original vehicle or really old NOS, most any new ECU WILL be 4 pin.

You can use a 4 pin box in a 5 pin harness, but not the other way around

Incidently, the "single" (or other half) of the ballast is the same exact circuity/ wiring as the old points setup. In fact in an emergency, if the thing quits, you can stuff in a breaker point dist. hook the wire to the coil, unplug the ECU and go

In today's Chineseoficianicated products, hard to say, but ECUs usually don't fail that often