Pull the speaker and check the internal wiring. I bought a
WM 4x10 once for cheap that wasn't working. One of the
leads had fallen off. I reattached it and it was fine.
While you have it out check the wiring at the input jack.
Use a volt/ohm meter.
Plug a cable into the input jack and check that both the tip
of the cable and shaft of the cable are continous to the
internal wiring.
Finally, disconnect one of the input leads of the speaker and
put the ohmmeter on in momentarily to see if current flows
through it. If it is blown out, you will have no current
through, likely a blown voice coil.
If the speaker is a cast frame basket, get it reconed. If it
is pressed metal, I would check with SWR for a replacement
cost first.
So, in summary, check all the wiring and connections first,
then check the speaker. Checking through the signal chain is
simply a process of elimination.
One Fender parts authorized dealer SWR CS referred me to
a couple of years back was Music Parts Guru in Chicago,
1-630-521-9170, contact I had was Corey.