If you have a preamp, and the volume pot is after the preamp, get a fixed resistor the same value as the volume pot, and connect that between the output and ground. That gives the load the preamp is expecting.
On a passive instrument you can do the same thing if you want the tone of the volume pot. You can also simulate a volume pot not turned all the way up with fixed resistors, or an easier way is to install a small trim pot for the volume control and install it inside the bass.
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