Water Tank Gauges for 1976 25ft Tradewinds

When I picked up the trailer from the PO he had a charger connected to the battery and the tank level gauges worked ( although I should have taken more notice of his surprise ). Since then I have not been able to get them to turn on. When I put the trailer in the shop for renovations, the serviceman did not seem to concerned about it and when I mentioned replacing them, I got the impression that he did not advice it and acted as though I could do without gauges. The more I think about it the more concerned I became.. The last thing I want is for one of the tanks to over flow (especially the black tank). So my question is two fold: 1) Have any of you replaced the water level gauges in your trailers? And, if so, how difficult and expensive was it? 2) Are any of you operating your trailers without functioning gauges? And, if so, how do you determine when the tanks need emptying? Also, if you are running without the gauges, have you ever had a tank(s) overflow on you? I really would appreciate your feedback to help alleviate this newbe's nerves.



Thank you

Txlogic