It's important to remember these things are diodes, not bulbs / globes.
Good ol' globes aren't polarity conscious, so they'll work as long as a positive and earth (negative) appear on each terminal in any order.
LEDs, OTOH, being diodes, are polarity conscious. If they don't get the positive feed on the correct terminal, they don't work.
Being POETS** Day today, I'm feeling too lazy to look up the 740's wiring diagram to see if the brake light switch supplies a ground to the brake lights' centre terminal to make them work, or if it feeds a positive to the centre terminal of the globe holder, which is the most common method.
In the latter setup, the light operates when +12V is fed to the light terminal via the brake light switch while the outer sleeve of the bulb / LED would be at 0V with respect to earth.
In the former (more unusual) setup, the outer sleeve would have +12V on it and the earth would be supplied via the brake light switch.
For a light bulb which doesn't care about polarity, this detail isn't important; for an LED, it's critical.
Do these LED replacement lights come in 2 flavours of polarity? (I'd hope so).
....oh, and the Bulb Warning Indicator? It's an electromagnet balancing trick with reed switches. It presumes that the current draw will be the same for LH and RH light circuits, so the little electromagnets in each circuit balance each other's magnetism out, and the reed switch doesn't operate. When one circuit fails because a bulb pops, there's a magnetic imbalance between the two, so the reed switch activates the bulb failure light. Simple, eh?
** POETS Day : Piss Off Early, Tomorrow's Saturday
