Right ive got a 1.9 diesel scudo van,and earlier the starter engaged without any key or anything(it was just parked up) it was in gear and started to leap forward then it stopped an smoke came from the bonnet!The smoke was caused by the earth from the battery to gear box melting,as it was shorting out(on the body)...would his cause the starter to engage?

Or it could of been shorting on the positive terminal of the battery...im not sure

Anyways ive replaced the earth cable but now i think the batterey's flat...or do i have another problem! Ive never known anything like this!

Please help i need to get is sorted!