Intermittent turn signals
 

My ‘65 GTO has all new wiring....dash harness, lamp harnesses, turn signal switch, etc. Turn signals will flash sometimes and other times will not . When they do work, they will flash a few times, then quit. Turning lever to off and then back on will sometimes cause them to work but just as ooften they don’t. There is no pattern to this, just a lot of lot of flipping the switch on and off and cussing. I’m familiar with the poorly designed lamp socket issues, lamp housing ground issues, etc with these cars, so I’ve already done that troubleshooting. I’m wondering where/how the turn signal switch achieves ground, since it appears mine has a very weak or tenuous ground. Does this switch ground through the steering shaft to the steering box and then to the frame? I may have made everything so pretty when detailing this area that I compromised any ground that is supposed to be achieved there. Or does the TS switch ground somewhere completely different?

Make sure the “Flasher” is working properly.

Turn signal switch doesn't ground. It sends power to sockets and through bulbs to ground. Flasher heats up to open circuit and cools off to complete circuit. Then cycle starts again. Make sure you have the correct flasher because it must match resistance of bulbs.

Intermittent turn signals
 

Took the known good flasher from my ‘64 GTO and plugged it into the ‘65. Still no turn signals. Plugged the’65 flasher into the ‘64 and no turn signals there either. The flashers appear to be identical: ‘64 is Buss Flasher 552/536 12 V. 32 CP Max 6. ‘65 is Littlefuse 552/536. 12 volt. 32 cp Max 6. Any other ideas about troubleshooting this weird problem?

When this happens, do the brake lights work?? If Brakes lights work and not turn signals then the issue would be either the power going to the turn signal
switch from the flasher, or no power to flasher itself. Bad fuse or bad connection at connector at bottom of column. Check break lights first. If brake lights don't
work, then you could have problem inside the signal switch. Yes i know you said it was new, But how new?

Here a link to the wiring diagrams from Wallace racing
http://www.wallaceracing.com/wiring-diagrams.php

Looks like power comes from the ignition switch, thru a fuse, onto brake lamp switch, splices off that terminal and goes to flasher, then to turn signal switch.
so need to do power checks along those spots. If brake lamps work, fuse would be ok.
Let me know if I can be more helpful.

Intermittent turn signals
 

Lemans64. PM sent