Brake Lights not working on AU Falcon Series 1

[VOGGA]

My falcon au series 2 has no brake lights when I hit the brakes. It lights up when I turn on the headlight switch. IT does not get brighter when I hit the brakes. Replaced the switch with a brand new switch. Checked fuse and is OK, Took it to a tyre and brake specialist and he said I have to go to auto electrician to get it checked out. Can anyone help me to see if there is anything else I could check?