i have just done this, and had to get a spark mate to make it for me, i just run it straight from the cig lighter to pump, u need to run both pos and neg, from cig lighter other wise it wont work properly
no probs up to yet, but only did two jobs to day, last week was fine, wish i had done it ages ago
I been using van battery since I started nearly a year ago. Its been fine apart from once where I left the doors open when working and interior light were on for a long time without moving van. I turn interior lights off now and been ok since, But bear in mind I have not got a full round, nor is it very compact so van gets moved regularly