1992 Mercedes 190 E lights and wipers go on by them selfs when it rains

1992 Mercedes 190 E mileage: 105,000. I have problems every now and then, mostly when it rains, I wash the car, or when the weather is heavy, my windshield wiper fluid and wipers on the front lights just go haywire. My original windshield wipers come on and my park lights come on, not all at one time but usually one or the other. I have taken the fuses out of the wiper fluid and the windshield wipers and kept them out to stop it from coming on, but the park lights still come on when something underneath the hood gets wet and stays on long enough to drain the battery. I was told that it may be the fuse box need replacing or a stuck relay but that was before I noticed the only time it does it is when it's wet. Do you have any idea what it could be? I thought maybe the fuse box top was not on all the way in the back which allows water to seep through but I don't know if that's were the problem is at all. I want to take it to the shop to get fixed, but when I take it it was never doing it and they were just guessing what the problem could be but now that I'm 99% sure it happens when it rains maybe I can get something a little more concrete. Please advise.