The pod motors must stop accurately when the pods reach their raised positions to correctly aim the headlights, so they use electrical braking in addition to 'hard' stops. The same circuit is commonly employed by power tools and electric lawnmowers to stop the blade quickly when switched off.
You may have noticed that unplugging a power saw while keeping the trigger depressed will allow it to spin down slowly, while releasing the trigger will cause it to stop almost instantly. That's because the trigger switch shorts the motor's power leads together after it disconnects them from the incoming power line.
When a motor is turned by its shaft (or inertia) instead of by its windings, it acts as a generator. The greater the electrical load on a generator, the more difficult the shaft is to turn. If the generator is trying to feed power into a dead short, it is very hard to turn, indeed. The motor/generator stops extremely quickly instead of coasting down. Most cars' windshield wiper circuits also use this technique to park properly.
The Wedge headlight circuit uses a pair of relays located near the fuse block behind the glove box to start and stop the pod motors. Located nearby is a single auto-reset circuit breaker that protects both relays and pod motors. If the circuit breaker is going bad, it may start getting tripped by normal amounts of current instead of overloads. The pods will randomly stop then start up again a moment later. If the ground circuit connected to the relay contacts becomes bad, the pods will raise and lower but they will not stop where they should, and may just keep going up and down. Corrosion in the various electrical connectors seems to be the main cause for failure, but watch out for bad gaskets letting water into the limit switch housings on the motor assemblies, too.
The Repair Operation Manual has detailed instructions for repairing and adjusting the headlight assemblies. When looking for spares and information, be aware that the first generation Lotus Esprit used the exact same mechanisms with different pods attached.