Fixed it... Coordinate system was not the same between the two readers, used Reprojector Transformer on both to put them in the same coordinate system.

Good to see you found the solution. As a general tip, the visual preview in FME Workbench (and the Data Inspector) will reproject data automatically, but that's the only place in FME where that happens. In your workspace process you need to ensure that data streams are in the same coordinate system if you want to geographically relate them to eachother.