Could be many things....
The way to approach it is to prep a cable with 1/4" jack (amp) to croc clips.
Start with the pickups- unsolder at the pots and connect to the amp with the croc clips - how do they both sound?
Next, wire pickup to a volume pot (disconnect tone pots) - does it still sound good - does the volume pot work as expected?
Next connect the tone pots (one at a time) - do these work like tone pots?
Next, the switch.... croc leads on the 'output' - do all three positions work as expected?
If all is good then so far you have two working pickups, two working vol pots, two working tone pots and a working switch OR you will have found some problems to fix...
Finally reconnect the output jacks - these are a flippin' nightmare on Rics with the whole Ric-O- Sound stereo / mono switching.
It's often easier to fully rewire than try fixing previous dodgy fixes.
I'm looking for a good Ric 4003 wiring diagram - best I could find is this... what you really want is a diagram with the parts and wiring shown as-is.