I actually work at a dealer and maybe I can help you. If you are talking about parking lights, does the problem get worse, the more accessories you run. Such as if headlights, blower motor and maybe wipers are on.
if so, you could have a possible alternator regulator not creating enough
power to supply all the accessories, therfore your battery voltage is low
and could be the cause of lack of power.

Thanks for your input 'ifixsprinters'. It seems like this is my first task to try and fix the problem, hope it works as I am so pleased with my van apart from this.