1985 BMW 325 fuse blowing

My car is repeatedly blowing the same fuse, I thought I had found the problem and after repairing the oil pressure wire connection and cleaning up the rubber boot covering it; it seemed to be my andwer. However after I test drove it, upon returning home the fuse blew again. It lasted longer than it has been doing in the past 2 weeks. I then went back under the car to look at the oilpressure wire again and again the rubber boot covering iet was filled up with black sludge oil. Could this be the cause of the problem? If so how do I safely clean and degrease the engine underneath and under the hood without doing any more electrical damage?