I replaced most of my interior lights with led. Whatever I was able to reach under the dash too.
Now a year later, driving with parking lights or headlights on. Intermittently when I brake or use my turn signal, they blink.

It’s very possible the plastic blue colored strip where the wiring plugs into behind the dash/ speedo panel is worn out.. it could be grounding every once in a while causing this problem..

LED's are a no load component and when the voltage drops in the circuit, they will do funky things like blink. Could be a bad ground as well.

These things happen when trying to integrate modern technology into 50 year old wiring harnesses and circuits.