Engine starts when cranking but stops when the key is released.

Hi guys. When I crank the engine it fires up straight away and runs, but as soon as I release the key and it returns to the run position the engine stops. I have only just recently bought the vehicle in this condition, so can not provide any history. The guy I purchased it from had it running in front of me a number of times. He had all the steering column pulled a part and was using a wire to short out the starter and started it that way. He also had some harness plugs pulled apart behind the battery box. I reconnected everything back up and got the engine cranking from the key, but now have this problem of it not continuing to run once the key is released. I am thinking now I that I have connected everything back up we are now back to what the original problem was.

I am definitely no great shakes when it comes to automotive electrics, but I have run a multi-meter over the ignition switch and the coil and power seems to be getting every where it should. Any ideas would be great guys. Remember though I am a bit of a novice at this stuff, so you will have to explain in basic for me.

Thanks in advance guys.