Intermittent click when key turned, won't start. help

[Jez Camber]

So, this has got more frequent. I get in, turn the key and there is just a click. not a stater motor click, just a click somewhere behind dash presumably. I have changed both clutch pedal switches but this did not help. if you try to start with clutch pedal up there is no click anyway so pretty sure unrelated to that. After a while it will start normally on the key. Plenty battery power, that side all tested ok. local merc van workshop suggests possibly CDI control unit relay or relays, there's 3 I am told. I am open to sugestions if anyone has had a similar fault. It happens with both keys so not related to immobiliser I don't think. Thanks in advance for any help.

 

[Flyinspanner]

Get a STAR diagnosis, it may be the EIS beginning to fail?