1999 vw LT46 2.5tdi campervan,?

Van 1st time starter and just had fullservice, and then put into reputable auto electricians to see why speedo not working correctly. They rang the next day, and said the speedo head not working, and needing replacement. I told them to put back as was, and I would look or replacement, when I got there and paid I was asked had I had problems starting the vehicle, and I told them never,as they had, and after checking battery power they tried the key again and it started. I got in and drove home, and left it in carport overnight. When I went out to it the next day and put key ignition panel lit up for asecond and everything then went off,ignition,radio,lights,indicators,haz… Yet when I flick foglight switch high pitched whistle can be heard coming from behind intrument cluster,when I turn off switch it stops. Also speedo needle whirs round to 180kph then comes back eventually. Do you think the auto electricians have nipped something or put terminals back incorrectlywhen putting back instrument cluster. No fuses are blown, and battery has 12.94 charge in it. This happened good friday morning, and they do not open until tuesday, as you can guess I am having a wonderful easter holiday. This was a minibus with tachograph whic is not used anymore, after it was converted to campervan.