How test 13 behaves
Test 13 lights every CPU lamp for only about five seconds, then fires each CPU coil once (not the T or Q relays), then shows any closed switch on the ball/credit display. A switch takes about two seconds to show, and with no switch closed for five seconds the game drops back to attract mode, so work fast or re-enter.
Systems
Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)