For the 66 and older vehicles, the 4 way hazard flasher units could be either factory installed or bought an as accessory. The factory installed units like this were hidden up under the dash, mounted vertically and you pull down on the red button to activate it, push up to turn it off. (The accessory units hang under the dash and you pull the knob towards you to activate it, push to turn it off.) This is a very clean unit. 100% of what you need to install it is there and I tested it on my own car. It works perfectly and the red knob flashes as it should. The 2 prong flasher unit is a later aftermarket flasher which is no surprise because the original flasher "cube" was a very poor quality unit.

This unit with this style of mounting bracket is made specifically for 1966 full size Pontiac, Beaumonts and Acadians as well as full size 1966 Chevrolet, Chevelle and Nova. It may work in other GM's that year as well but I can't say for sure. The signal switch on the Pontiacs is the same from 1964 - 1966 and this unit plugs in between the body harness and the signal switch harness so it must work on 1964 - 1966 models. 

  The first picture shows how it connects to the signal harness.  It's very simple to install. Mount it under the dash (I can get you a picture of the correct location from my Strato Chief that has a factory installed hazard unit), disconnect the signal harness from the body harness by the steering column, plug one side of this unit to the signal harness, plug the other side into the body harness, plug the orange power wire into a live 12 volt source at the fusebox and it's installed. It really is that simple, yes!

Asking $125 plus shipping (Canada Post flat rate box is $18). I'm located in Morris Manitoba.