Once the hardware is in, the manual guides the technician through a series of "bench tests" while the aircraft is still on the ground:
The last 20 pages of the S-TEC 55x Installation Manual are a goldmine for troubleshooting. Here are three common post-install issues and their manual-specified fixes: S-tec 55x Installation Manual
The are the most referenced pages in the manual. For the SC-55x (50-pin D-sub connector): Once the hardware is in, the manual guides