You are right to be worried about the electrics! My first tank had a 'built in' light, filter & air pump system. There was a plastic lid over the actual lightbulb but nothing protecting the sockets or wiring. Within four months the sockets failed, I took the whole thing apart and realised that all the wiring was completely corroded (and probably very unsafe). And of course I'd lost the receipt by then...
The answer is to buy a condensation tray, basically a sheet of corrugated, clear plastic. About £3, various different sizes (which you can cut down if necessary). As well as stopping condensation from damaging lights they are also a good safety precaution in case your light fixings perish & the live bulb falls in the tank. Most lamps say in the instructions that there must be a barrier between the lamp and the water for this very reason.
I had to take out the lighting unit & filter and replace them, which was annoying. I then bought a small condensation tray, cut it to shape (my tank is hexagonal so that was a bit tricky, but I managed okay) and since then I have had no problems whatsoever. I also have one on my big tank. I cut a square hole for feeding and used offcuts to make little 'hatches' that I slide back and forth.
