Electrical short
While still fiddling with the carburetors, all of the sudden I had no power
whatsoever when turning the key to start the car. All electrical was not working
(including the headlights). After checking wiring harnesses, battery terminals
and such, I discovered that the screw that attaches the wiring harness to the
body (next to the battery) was loose. After a good cleaning with a wire brush
and tightening it back down everything worked fine.