solanoid?

I have a Peugeot partner 2001 x reg 1900 .The thing is there is a plug that fits in to the solanoid for fuel pump when starting the van i have to push plug in and clip down'i then have to turn engine over then go back to plug and take out 'you can then here the engine kick in properly.once the engine has run for a while it will start all day.I bought the van of a freind and he explained this before i bought it but is annoying me asked allot of people about it but no answers as of yet.Any pointers would be great as i have not a clue about cars ,vans ect.