Sounds like it might help if you got a 4A wiring diagram.
Otherwise, use an ohmmeter or continuity tester to check out all combinations of switch terminals/wires in each switch position. Write down which ones show continuity (0 ohms) in each position. I like to do this anyway, just to make sure I have the right switch. For example, there are at least two different versions of that 8 terminal monstrosity used for headlights on the TR4, and they aren't the same! Vendors also sometimes supply the wrong switch.
You should come up with a pair of terminals that show continuity in the first position (parking lights); and a third terminal that shows continuity with the first two in the second position (headlights). Should be another pair that only show continuity in the spring-loaded "flash to pass" position.
From what I've heard, there are some variations in the cars, perhaps based on the original destination country. In most cases, the "flash to pass" feature lights the filaments selected by the dimmer switch (which means it does nothing if the lights are already on). But sometimes, there is a UW wire that comes to the main lighting switch, so FTP can always work on high beams.