1964 BRAKE LIGHT RELAY.
The 1964 Thunderbird brake light relay has become obsolete from Ford and is not being made by any other after market manufacture. This is definitely going to create a problem for you people who own 1964 Thunderbirds and have this relay in your system.
I do not know of any replacement for this relay. I only know how to bypass it so you can still have brake lights.
The brake light relay is located on the left (drivers side) inner fender of the engine compartment just behind and to the rear of the windshield squirter reservoir bag. The relay has four wires, one ground wire and three wires going back to the brake light switch. The brake light switch is located on the master cylinder.
There are two wires that come out of the firewall (for the brake light system) just to the right of the brake booster, almost in the center of the firewall. One green wire and one green\red wire. They plug into the brake light relay loom. Two wires split off and go to the brake light switch and three wires go to the brake light relay.
There are two ways to bypass the brake light relay. You can either remove the brake light relay wire loom altogether and run the two wires coming out of the firewall (green and green \red) directly to the brake light switch or you can bypass the relay by jumping two of the four wires at the brake light relay plug.
See attached illustration to locate the four wires on the brake light relay plug. Make a jumper wire that will plug into the green \ red wire socket located at the narrow end of the plug and into the green wire socket located at the wide end of the plug.
Special tips: You should use the original plug at the brake light switch if you chose to remove the brake light relay loom completely. You can splice it in nicely using plain butt connectors (ones with no plastic on them) and shrink tubing. If you can find green shrink tubing that's good. However, I have not been able to find any so I use flat black. Try to make your splice after the separating plug. This way you can unplug the wires if you need to.