Turn Signal Troubleshooting
 

I've made some good progress on my '66 912's turn signals, but I'm not sure what to test next.

To begin with, my turn signals didn't work, I had headlights and brake lights, but no tail lights and running lights. I pulled all the housings, checked and replaced bulbs, cleaned sockets, replaced the terminals from the body to the light housings, and it's much closer now, but not quite right.

All lights currently work, and they're brighter than they were previously. I have my running & tail lights now, and the turn signal lights work. My issue is that try to activate the left hand signals, all four signals flash, and when I try to use the right hand signals, again all four signals flash, just like hazard lights.

What's my next thing to look at?

Have you replaced the flasher unit itself?

not saying this is your problem, but i had funky signal operations on my car when a single filament bulb was installed where a dual filament bulb belonged. The single contact on the socket end of the bulb was making contact with both prongs causing a lights to behave very oddly. Make double check that the sockets match the bulbs intended purpose.

I have not, I'll have to order one and see what happens.

Interesting! I believe I have the correct bulbs all around, but I'll double check so I'm 100%.

Is your wiring stock otherwise? I have found when building a harness from scratch or using a Painless version I had to install diodes between the turn signals and hazard switch to fix exactly what you describe.