[Leonard williams]

I have 1968 gto wiring problem,the tail lights,brake lights and turn signals work fine until i turn on the head lights, The blinker stops blinking inside and outside front and rear, also the brake lights will not come on brighter when i press the pedal. Has anyone had this issue

[LATECH]

you have a bad or missing ground somewhere. Check/clean them all.Start at the battery with the one that goes to the body and work your way back.
Make sure you have one from the engine to the body also.After that you should have cleared up a bunch of the problem, then go to the individual bulb and clean/check them for bad grounds or bad sockets at the bulbs that are still not functioning correctly

[ogre]

your tail lights and brake lights have nothing in common other then they're on the same car.
first off i'd start checking grounds, use a test light or meter to see if you have power at the lights.
then check the output of your tail lights at the switch; on and then with the headlights on.

your brake lights and blinkers are on the same circuit.
do the same test to see where the power quits.

you could have a couple of problems or a single ground that is messing with you.

[1badLemans]

Funny I have a 69' lemans that i just fixed a brake light wiring issue similar to yours a couple of days ago. Yes i had a bad ground where the light socket meets the ground "chain" link. I used a red scotch bright and bingo, they're working.