Sorry, meant to ask. It might be a silly question but will a dodgy earth lead prevent the dash lights from coming on? I can understand it would create a starting issue.
Depends which earth strap you are talking about, Phil.
The battery earth strap connects the negative terminal of the battery to the chassis of the car, and so if this fails you'll get no electric current anywhere. The engine earth strap connects the engine to the car. It's needed because the engine mountings, being rubber, will isolate the engine.
So yes, if the engine earth strap has failed the dash will light up but the engine won't start. If the battery earth strap has failed you'll get complete electrical failure.
