This bass was crackling and one of the volumes didn’t appear to be working correctly. On inspection I found one of the pots was loose and more importantly there was no ground wire on the output or between the pots. This was not a mistake as on a bass like this the grounds are linked through the control plate. The problem occurs when the pot with all the grounds on becomes loose and the connection to earth gets broken. I added a ground wire to the output and linked the pots to avoid this issues happening in the future, I also tidied up some repairs that had been covered with electrical tape with heat shrink.