Hmmm. That would make it a coin-toss, as to whether the wattmeter had a rotten ground on the coax sockets, OR the coax jumper had a rotten ground connection to the cable's shield braid.
--- OR --- maybe both of them were screwing up the antenna's ground circuit?
Odds are that the Northpoint uses the same 9-Volt regulator circuit that the other 'export' radios use to regulate power to the PLL and the crystals. Having to run the motor indicates that this regulator is set too high. Not so rare.
Either 'tweaking' a resistor in that regulator, to turn it down to 8 Volts, OR putting a 7805T chip in its place will usually permit you to use SSB with the motor off. Trouble is, this will reduce your PEP on transmit by as much as 10 or 15 percent.
Or you could just run the motor when you're talking sideband.
73