Reverse polarity warning light on in caravan

Octavedoctor

Hi folks...a bit of advice and help if poss, please......been using our 2006 Avondale Mayfair all year with no problems. Last outing 2 weeks ago in Wales, we Hooked up the electrics as usual, but had no power. Checked every thing, and found that the reverse
polarity warning light was on on our distribution board. Had the site manage check their mains supply, all ok...tried different hook up posts, no luck. On my return home, I connected up to our mains supply....same thing.....reverse polarity warning light on....no
power......any one got any ideas how to fix this, as it doesn't seem to make sense........