clio 1.5dci warning light/starting

iv'e got a clio 1.5 dci with a engine management/glowplug light on permanently. it is becoming increasingly difficult to start but runs fine afterwards. i thought i'd go for the easiest option and try the plugs. i connected a wire from the battery and touched each plug in turn but there wasn't a spark from any of them, which to me means they are not conducting anything. the engine has done 118000 miles. does anybody have any advice on my problem and does my simple test mean that the glowplugs are all duds.
any advice appreciated

my clio is doing exactly the same thing? did you solve the problem? your help is much needed


thanks