Leyland daf 130 45 horsebox?

Hi my horsebox has started to fail to start intermittently. It went to garage and I had starter motor reconditioned and new solinode. The wires were checked all ok. Started so had it back. Started for shout to weeks, stop start in different places on journey. Came to come home nothing just a click. Breakdown came and overrode it and we came home. Stopped when got home. Tried to start again nothing. Following day started 5 times so took back to mechanic who has checked it all again, but it's starting fine.
I'm worrying if I go out it won't start to come home. He has put a wire on for me to start it myself just in case.
I want it to be solved. He thinks may be something in dashboard. Any ideas please thank you