It also looks like the red and orange wires have been disconnected and they wrapped the ends (with something blue on the end of the orange wire and beige on the end of the red wire?). Am I seeing that correctly? Or is the orange wire connected to the red wire (hard to tell from the picture)? On CDK's pic, the red and orange wires are going to the 1/4" output jack (as well as a blue and black wire, which yours still has connected). So I can't tell where that stray black wire is coming from or where it's supposed to go. Perhaps it's been rewired such that your battery is on all the time.
Also, look at the slightly thicker black wire that goes from the XLR jack, and then (behind the circuit board) up directly to the bridge pickup. Hard to tell, but that's what it looks like in the picture. CDK's picture doesn't have that at all, it has the capacitor instead from the XLR to the 1/4". Very strange.
Does your DI output function properly? If the DI does work, does it work without a 1/4" plug inserted? On a correctly wired Wal, the DI won't work unless there is a plug inserted into the 1/4" jack (which turns the battery on). If your battery is on all the time (which IMO seems to be the case), you would not need a 1/4" plug inserted while just using the DI out.
Ok, I just opened up my Wal and figured out that (upon inserting a 1/4" plug) the red wire makes contact with the orange wire in order to turn the battery on. The blue and black wires on the 1/4" jack are just the two normal wires that make contact with the cable when plugged in. There is usually a capacitor (as seen on CDK's picture and missing from your bass) that goes from pin 1 of the XLR to the black (ground) connection on the 1/4" jack. Your bass has a black wire attached to the XLR that seems to go up to the bridge pickup (maybe for a ground connection to the metal casing of the pickup?).
So, my guess is that a previous owner replaced the 1/4" output jack (to alleviate crackling noises from the 1/4" jack, which is a common issue with Wals), and they connected the orange and red wires together to leave the battery permanently on. Are those red and orange wires (with the blue covering) connected together? It's hard to tell from your picture, but I'm guessing that they are because that's what turns the battery on. And that black wire that appears to go from the XLR to the bridge pickup must be a ground of some sort.
This is interesting, please keep us posted with your findings.
