I tapped onto an existing hot lead and ground that didn't go anywhere on my boat to install fishfinder. Finder turnedon for a few seconds and went off. Also stereo now turns on for a momentand then flashes also lighter plug works for a moment and then stops. I took off the splices to those wires but problem with stereo and lighter plug persists any help would be appreciated

You got fuses installed in the lines? Finder definitely needs one.stereo would also need one...general use plug could benefit from one as well...separate fuses of appropriate ratings for each item.