electric --blown fuse 1975 240D

I have a 1975 240d, I am restoring it, I have put in new brakes, new engine (used) etc, I am working on the interior now. I was testing out lights, etc when I turn on the wipers the fuse blows and blows after I replace it because I dont have enough time to turn them off before it blows. I dont think it is the wipers for they work before without a problem. I think its in the horn (which I have done nothing to) or the cig lighter. I assume it/s something on that circuit, horn, cig lighter or wipers. I would appreciate any suggestions. I do not have a drawing of the wiring, so where do I start????? since it blows right away, I assume I have a short somewhere???
tks in advance. this is the last item to corrrect, then I can get it inspected and on the road. Don