Soldering iron, solder and meter for EM games
A 25 W iron is enough for EM wiring. Use 60/40 rosin-core solder; lead-free 95/5 hardware-store solder does not work well here. Buy a digital multimeter with an audible continuity beep and good low-ohm range, and keep a few long (12 to 18 inch) alligator clip leads for jumpering contacts and lamps.
Systems
Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part One, Clay Harrell (pinrepair.com)