Literally spent all day trying to run a NMEA backbone cable from the engine room to the helm on my 370 DA. Found a tube which looked like it would work -- already had a few shift cables and a transducer cable from the previous owner. It's a black flexible plastic hose. Well now I am stuck with about 2 feet to go. Can't pull the cable thru. Can't get it to come back either. So close but so far. What's the trick?