side lights are a seperate bulb, sometimes a w5w capless, sometimes a 6w capped.
You should just be able to pull the HID bulb out, disconnect the ballast and shizz from the wiring loom, then plug a halogen bulb in.

Remove all this
Then do this

You should have one of these connected to the power supply on the ballast

Plug that onto the back of the new halogen bulb. Job done