As far as I can tell from Hugos posting, a 1kOhm 1/4W resistor between the antenna control line and ground should do it. Exactly where it is placed is irrelevant as long as it goes between those two things. I'd put it where it's the most convenient; either by the motorized antenna or by the plug that plugs into the tuner module.

Havent looked too close at the plug, but most likely the actual contacts can be removed from the plug, the resistor legs solderd to the appropriate contacts (the crimp area - don't overdo the heat) and the contacts put back into the plug.

The contacts usually (as I said, haven't looked to closely at this specific thing) have a small tongue that needs to be depressed with a really tiny screwdriver (jewelers type) or needle or somesuch to be able to be pulled out of the plug...

You could also put it in somewhere where you connect these wires anyway - like where you connect the blue tuner wire to the cars wiring - just make sure it's goes between antenna control and ground.

Probably a good idea to isolate the legs of the resistor with heatshrink tubing.

/Michael