check the earth from the gearbox/engine to the body easy way of checking is to connect a single jump lead from the engine good earth point directly to the NEGATIVE SIDE of the battery this will eliminate any bad earths then check you have a good 12v live on the main thick starter cable then a 12v feed on the smaller trigger cable when you turn the key to start.hope this helps
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.