Turn signals activate horn ... sometimes

I have a 73 Dart Sport. I just got it and it had some issues. The steering wheel was delaminating and the wood was moving under my hands, there was no horn at all and the wire was just sticking out of the wheel hub because the horn kit was missing, and the turn signals wouldn't cancel. I bought a new cancelling cam and installed it. I soldered the wires and they are insulated. I replaced the steering wheel and installed a horn kit and also replaced the horn. It all works. Two days later, coming home from work at 3am, I hit the left turn signal and the horn starts beeping in time with the flasher. The next day, it all worked fine again. Last night it started honking again, and this time I noticed the headlights seemed to dim with each flash. I am thinking a ground somewhere because if it was a short to power you would hope a fuse would blow. I have some online wiring diagrams that really suck, so I ordered some new ones. I am hoping to fix this before the weekend, however. Anyone have any ideas?