Here some info about wagons, that could be connected with ET 89:
- Di-el24, open end, green livery, later renamed to EB 89
- Bi-24, open end, later renamed to EB 89
- BCi-24, open end, later renamed to EB 89
- Ci-25, open end, later renamed to EB 89
- Di-24, open end, later renamed to EB 89
- Cdi-23, open end, later renamed to EB 89
- Pwi el-29 (rebuilt from Pwi-29a), later renamed to EB 99
All of them had steering cable (Steuerkabel) so it's possible to build train consisting ET 89, 8 wagons and second ET 89.
I think the names means:
ET - elektrisch Triebwagen (ET 89)
ES - elektrisch Steuerwagen (ES 89)
EB - elektrisch Beiwagen (EB 89, EB 99)
ET 89 could pull up to 4 wagons EB 89. I found an info about consists of 3x ET 89 with 12x EB 89.