Just made up this new box after successfully trying out an earlier prototype . This plugs into the existing Mercury factory wiring between the engine harness and ECU . All 16 of the inputs/outputs connected to the ECU can be monitored at there own color coded test jack plugs with a multi-meter and DVA adapter (for the cranking tests) . Continuity tests between the factory connector back to the sensors or devices connected to the engine harness can be run . Cranking and running spark coil voltages can be checked as well as injector pair pulses/voltages without the need for the merc injector test cable .Resistances of the manifold air temp sensor and coolant temp sensor can be checked . TPS calibration can be checked and adjusted without the special merc test cable by unplugging the engine temp sensor and moving the throttle 0-100% . Using this box I can run down all of the associated ECU I/O very quickly and got all of my baseline reads on a running 200 EFI . Fuel pump voltage and current can also be monitored at jack plugs for this purpose .
The box itself is 6 x 9" so I figure I can carry it along with me in the boat and if the motor gets hard to start check out all of the ECU sensor values . I put 3 foot leads on so I can drive the boat while monitoring things . I know Mercury has a DDT tester that can do all of these tests but I just made up this thing as a cheaper troubleshooting alternative .