Originally Posted by P Town
It's the cable.
or perhaps the jack in the bass. The active preamp turns on by the "ring" contact which on a mono cable simply shorts against the body of the 1/4" plug which turns on the battery. With a stereo cable the "ring" contact will connect to the "other" wire in the cable which will likely be floating and not turn on the preamp.
So either you are trying to use a stereo cable (which will not short the battery to ground and turn on the preamp) or the bad cable has some corrosion on the body of the plug that keeping the jack from making contact and turning on the preamp, or the jack contact has lost tension (very common) and doesn't have enough tension to make contact if the one cable is slightly less than a 1/4" in diameter (some cheapo and some expensive cables are slightly off from standard size for unknown reasons. I guess somebody thought it made it "better".