Originally Posted by JABS
Use multimeter to check the resistance between the centre and scree on the plug. it shouldn't be zero, but I don't know what it should be.
It may well read zero or, at most, the resistance of the cable. Many VHF antenna are of the 'J' aerial type and these will have both conductors connected at the bottom of the J so will appear as a short circuit to a resistance meter.
Have you mounted the antenna to the boat? If not, simply hold it and connect it directly to the radio so you know there is nothing untoward about the connection. I suppose it is possible the new antenna is faulty but it's not likely.
It is very easy to make a working J-antenna for test purposes. A bit of wood (garden cane or something similar) a length of wire and a bit of 50ohm co-ax with a connector for the radio. A couple of terminal blocks can be used so you don't need to make solder connections.
I'll post details if it's any use to you.