Did GM offer (factory or dealer installed) a Hazard Flasher option for '64? I know F*rd did for the '65/66 Mustang as a Dealer Option, standard in late '67.

Any such animal?

I have an aftermarket one installed in my 64, it was such a butcher job, I removed it and may not reinstall it. I had RichL79 email me a copy of a diagram of one for his 65, you might try to email him too.

Don't have one on my 64 and can't remember seeing it in any of the RPO sections in the manual.

I don't think there ever was an RPO for it. It was only dealer installed as far as I know. It was available in 1964 on all GM A-bodies. Various versions were used and the Buick and Olds versions used unique wiring plugs while the Pontiac and Chevy versions used the familiar half-moon style plug which matches the steering column plug.

E-mail me if you need pictures. I have a very good one that came with my car that I have not installed because it gets banged by my knee if it is in place.