G4 12v LED bulbs won't work?

I bought some G4 12v LED bulbs as replacements for G4 12v 50w halogen bulbs. They go into garden lights which are switched by a normal indoor light switch. I can't get any of the new LED bulbs to work.

The pins on the bulbs seem slightly thinner than the halogen bulbs so they may not be making a connection. I've tried bending them to try to ensure they make contact.

There is no timer or other posh controller for these lights, so the issue isn't that the LEDs are incompatible with a switch which expects a load.

I'm out of ideas. Any help appreciated.