With Lego back to 1991 again: 9V train set 4563, flat bed with tractor 4543, tanker car 4537 and level crossing 4539. Still cobbling together some parts, but getting there. - 9GAG
Lego 9V Electric System (4548): Amazon.de: Toys
9V | Brickset: LEGO set guide and database
Great Ball Pit: Lego 9 Volt Train Speed Regulator 🔌⚡️