This thread should be in the main forum. All the major mustang vendors sell parking brake warning light/switch kits for the '65/66 cars. You won't even have to drill a hole in your dash.
I suppose, that if you made a bracket and drilled a hole in it, then you wouldn't have to drill a hole in your dash. However, this was not Ford's intent. See attached copy of the Instruction Sheet (IS 1311) that came with the original Ford Accessory.
NPD has a kit for it
over here.
Since it's a repro of an original Ford accessory you can just tell anyone that asks that it's a rare factory option. It's even in the 60s accessory catalogs: 66 (in French) and 67.
The price has gone up a little since the 60s though. It's now $58.66 versus $3.70 if you would have ordered it back when the car was new.
The first part of this statement is correct, that it is a repro of an original Ford Accessory. However, the comment of it being a Factory Option is incorrect ; this was never offered as a Factory Option Remember, Factory Options were ordered when the car was ordered and installed at the Factory ; Accessories were available at the Ford Dealer Parts Counter, and either sold directly to the Owner, or purchased by the Owner to be installed by the Dealer, which some call "Dealer Options" (I personally avoid this term so as not to confuse it with true "Factory Options", which are usually referred to as just "Options").
Finally, the last statement that this Parking Brake Warning Light also appears in the 1967 Accessory Catalog warrants additional clarification so as not to steer readers in the wrong path. While the picture in the 1967 Accessory Catalog shows a warning light that looks like the same one as for 1965-66, the 1967 version was considerably different. Remember, Accessory Catalogs were printed before actual Model Year Introduction, so they would be available at that time. Thus, many times, pictures of final production details were not always available. The 1967 Mustang Parking Brake Warning Light carried a new Part Number, specifically for Mustangs ; C7ZZ-15A852-A. Its physical appearance was now a round plastic lens, approximately 5/8" diameter, and about 3/8" tall, with a round chrome ring about 1/4" tall around the base. I don't have access to my actual part right now, but a copy of the Instruction Sheet (IS 2549) that I have attached will give you an idea of what I just described. Interestingly, the price shown in the November 1, 1966 Ford List Price Book remained at $3.70. Since I don't have anything earlier than the November price book to document the existence of the C7ZZ warning light, it may be
possible that the 1965-66 versions were sold before then ; however, I don't believe that the curvature of the 1965-66 chrome housing would fit the 1967 dash.
Hope this helps.
Bob