The OEM speaker wiring is flimsy rubbish, so if you are upgrading the stereo system, you will need to replace it with something more substantial.
"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"
'80 Triumph TR7, '73 Land Rover (Ford 351. V8),
'97 Ford Falcon Longreach 'S' ute,
'98 MG-F, '69 Ford F250.