Because of the comments on the Radiator WIKI-page, https://wiki.jenkins-ci.org/display/JENKINS/Radiator+View+Plugin, I replaced the Radiator Plugin with the Build-Monitor Plugin.
First it didn't work with Build-Monitor, because the Jenkins Server root directory contained several Jenkins Configuration files from many previous releases (I'm maintaining our Hudson/Jenkins Server since 3.5 years). This was not so “obvious”. I realized it by using Build-Monitor with a fresh installation, which worked perfectly. So, the Build-Monitor plugin only started working after removing all the config-relicts.
One major drawback: Jenkins 1.374 and Build-Monitor Plugin only work with recent Firefox and Chrome browsers. IE10 and IE8 are not supported. In IE11 you can't change the text-size, so it's not usable if you have many jobs in your view. Issues I didn’t have with the Radiator-Plugin, which was OK with IE8.