Hi Dek when you say installed a new ignition switch this must mean you have a new key now as well, if so and this van has an immobiliser built into the ignition ie not the keypad type then this is where your problem lies. In order for your van to start the key plus the bsi (under the passengerside behind the glovebox) plus the brain must all be programmed to each other therefore if you change one of these units you must change them all or else take it to the dealers although its probably cheaper to replace them most breakers will sell you all three from as little as £200. I know that may seem alot but try going to a dealers with that problem and you,ll see what i mean. Hope this helps
Kevin
June 2009