had similar to this on escort,had a good look with magnifying glass,turned out to be live side of fuse blade holder had dry joint,[was cracked solder] where fitted in fuse box.was able to strip down fuse box and re-solder,but not sure on your vehicle.you may be able to fit a fresh fused ignition live lead to heater.
k
August 2013
There are several circuits on motor vehicles that do not operate until the key (ignition) switch is operated - wipers for instance - a relay is energised that feeds power to those circuits. The relay on your van that does this may be defective.
Peccavi
August 2013
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