Hello Simon, Welcome to justanswer...
Brake light switches are a common cause if this problem whereby all the lights come on together..
The first thing to do is check that the brake lights work - if not - that is a definite cause...though not 100%... ( ie, the brake lights can still work but the switch circuitry faulty)... but its worth checking.
Second, check the connections to the switch... ensure they are all good... Third, if the brake lights dont work...be sure to check the fuse for them ( its location is highlighted on the fuse box lid ) ...replace if blown -or poor connection.
If all the above checks out - replace the brake light switch first. They do go faulty often so it wouldn;'t be a total waste ...but also this is your most likely, and cheapest way forward.
That should cure this problem. IF you still get it - the van is going to have to go on a diagnostic machine to see whats going on... but try the switch first - as I say, its a common issue.
I Sincerely XXXXX XXXXX have helped you - Please ask me if you need more help...
Kind Rgds,.... MIKE
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