Converting combo to head, wiring help needed!

Hi guys, I've got a 1x12 Fender Performer SS amp I'm going to convert to a backup head to run with my 4x12, but I've hit a snag - the combo speaker is hardwired into the chassis.

The amp has an 8ohm speaker out jack as well as the hardwired combo speaker, so if I just cut/disconnect the wires to the combo speaker and use the speaker out jack will the amp work alright, or would this damage it?

Alternatively, if I have to keep the combo speaker wires attached, I suppose the best thing to do would be to attach a female jack connector to the end of the wires and run the amp like that - however, what would the process be for doing this? I'm aware it would be a 5 minute job but don't know where to start!

Thanks in advance for your help!

I would put a switched jack socket in, then if you put in a jack - current is routed to the jack cutting current to internal speaker but if if no jack present current goes to speaker. I put one in my amp the other day, it was simple but I did need a continuity buzzer to work out what contact was what. I believe that signal (+) goes to the nipple bit of the jack and earth to the outer sleeve.

Thanks man, sounds promising and easy enough - however despite years of modding guitars I've never done it with amps, if you would be kind enough to do an absolutely idiot proof step-by-step I'd be incredibly grateful!

Drill and fix this in the back of your amp. Cost about a quid.

4R is - from amp
5RS is - to speaker
3T is + from amp
2TS is + to speaker
S1 is nothing

Place an unattached jack in the socket to find out which contact is which. Hence the continuity tester.