With local train have a look at
http://www.rheinbahn.de/mobile/fahrplanauskunft.html
There is an hourly train whichs links Wuppertal and Dortmund directly. Sorrowly costs about 15 Euro one way (clase D)
Von: Wuppertal, Hauptbahnhof
Nach: Dortmund, Hauptbahnhof
Datum: Mo., 18. Sept. 2017
Preisstufe: D Erw. 15.00 € / Kind 1.60 €
ab 09:02 Wuppertal Hbf 2 Karte
Zug R-Bahn RE4 Richtung Dortmund Hbf
an 09:51 Dortmund Hbf 20 Karte
Benjamin M.
@Colamann德國北莱茵-威斯特法伦杜塞尔多夫
In case it's still interesting, the train in question is the Regionalexpress 4 (or RE 4), and leaves every hour at two minutes past (12:02, 13:02...) from platform 2.