Positive

hi all please if you can help me that would be great,i have a fiesta 51 plate 1.8 turbo diesel ,i purchased from someone who had been driving the vechile every day ,he left the vechile sitting for around 3 months before i took it off him as an non start,the car has a new battery,i have checked all the feeds to the starter motor which was fine and made my own earth connection with a jump lead,so i replaced the starter and nothing has happened still it just makes a clunk noise from the starter solenoid,i then tried to turn the engine over by hand,it was very stiff clockwise but when doing anti clockwise it is free and turns over fine that eliminated my suspicions of a seized engine ,ive checked all earths on vechile and have checked all fuses in the engine compartment and in the o/s/f inside the vechile,today i decided to take the glow plugs out and replaced them with new ones,before putting them in i put a bit of oil down each cylinder,and tried again to start vechile it started to turn over but slowly i managed to get it cranking over in slow stages until i noticed that the postive lead from the battrey to the starter was melting and the starter motor was very hot,ive yeat to try any easy start but will do a,s,a,p has any 1 ever come across this problem it was a runner ????????????? ive also tried to jump start vechile at 40mph

BEING A VAUXHALL MECHANIC I DONT KNOW F**K ALL ABOUT THESE ANY ADVICE WOULD BE A GREAT HELP