Vintage ESC

[Brat]

Hi guys, I've got a vintage Sanwa Vortex ESC. Tried it on yesterday and realised that it cannot work without the 4 'AA' batteries to the reciever. Open up the ESC and noticed that the copper plating from the on/off switch wire to the red wire leading to the reciever is burnt.
Can any one advise me if the power source from the stick pack need a resistor before going to the red wire to the reciever. Or will the reciever get burn if a i solder one of the on/off switch wire to the red wire? Thanks.