Re: Odd question ... Honda GL 1800 ... HID convert
Honda uses nonstandard versions of bulbs sometimes. On my old GL1500, the bulbs were specified as being H4, for example. But the little tabs and notches in the shape of the base of the bulb were NOT the same as off the shelf H4. Honda apparently does this to force you to buy bulbs at the dealerships at a premium price. What I found out when I was ready to replace them was:
1) a little gentle Dremel work on the bayonet-style socket in the back of the headlamp housing that the bulb locks into was sufficient to allow off the shelf bulbs to lock in securely.
2) For the American market, Honda installed 35 watt halogen bulbs, but elsewhere in the world, they use 55 watt. Same headlamp unit, part numbers, etc. Guess which wattage I installed!
So while I have no experience with GL1800s beyond a few test rides, it is possible that a weird bulb variant is required - thus involving your gift-receiver in something a little more involved than a plug and play install. On the other hand, perhaps converting to HID on one of these is already so much of a project that this would be a drop in the bucket.