Adding Speaker Out to Gibson Skylark

[vortex]

I want to put a speaker out jack on the chassis of a Gibson Skylark GA-5T combo so that I can easily hook it up to different cabs. Currently the amp has the speaker directly connected from the OT to the speaker.
If I route the speaker wires coming from the OT to a standard metal 1/4 inch jack drilled through the chassis, does the jack need to be insulated from the chassis?
TIA
Vortex

[vortex]

OK, never mind. I've figured it out, the jack had to be isolated from the chassis.
Thanks.