Building a Minimal Bench Harness for a MEMS ECU

I am often asked: What is the simplest wiring harness needed to allow me to program or test a MEMS ECU on the bench?

The designs for the bench harnesses I use are documented within the article Building a Key Programming & ECU Immobiliser Testing Interface, but those include the immobiliser connections and other facilities such as injector and ignition coil indicator LEDs which are useful when programming key fobs etc. but not strictly necessary when just programming or testing the ECU. The diagrams below show the absolute minimal bench harnesses which allow the ECUs to be powered and to communicate over the OBDII port: