Engine quits

I'm pretty green in the electrical area but would like a little assistance. My friends boat kept shutting off when a wave hit the boat at the dock or some other movement on the boat that was made. In checking all the wiring behind the gauges and ignition, we pretty much boiled it down to it being one of the wires coming from the ignition witch. The wire from the switch ran into some sort of plastic housing sleeve about 2" long with electrical tape over it. We ran out of light last night and didn't' take it apart. Before we head back to dock, I want to be prepared to try and fix it. Does anyone know if this sleeve may hold a fuse or do you think it is some kind of housing used for splicing the wires together. Thanks in advance