Yes, the 20B uses an external injector relay.  This is optional (it says so on the schematic, but Tracy recommends including it) and can be left out if the builder does not want to be able to run only on primary or secondary injectors in case of an emergency, such as one injector decides to quit working.  It uses the Cold Start circuit to double the flow to whichever bank of injectors are chosen.  Pretty clever, but rather confusing to wire.