Q: Engine and lights not turning off when turn key to fully off

Hi the van is actually a ford ecconovan but there was not the option for this make. So I have had a variety of issues with this van but the current issue I am having is that the engine won't turn off when the key is turned to the off position and taken out. We have been having to stall the van and disconnect the battery everytime we stop driving. We temporarily fixed the issue yesterday by spraying some WD40 in the key hole, although it didn't work at first, we were topping up the oil and remembered we had forgot to disconnect the battery as it hadn't worked and then noticed the lights were off, so we turned the van on and off a few times and all was fine. Then again this morning I went to grab something and noticed the lights were on again so we tested with the key and the engine is back to not turning off again. I don't know what to do as taking it to a mechanic is likely to cost a lot of money which I don't have, and I don't know anything really about vehicles. Hope someone can help
My car has a manual transmission.