The original squarebird clock is an electrical/mechanical wind clock. It doesn´t draw a constant current. As soon as power is applied to the clock, it will wind a spring in a fraction of a second, where after it opens its electrical contact. The spring will move the clock for about one minute and 15 seconds, where after the contact closes again and the spring is wound again. etc etc etc.
The clocks fuse is 1 Amps, so expect a current draw of 600 m Amps or so. But as said, its only a current draw for a very short time, which repeats itself each one minute and 15 seconds.
1958 T-Bird "Trovão Rosa" - "Rose Thunder"
Thunderbird registry #61670