I don't recall ever having to replace a headlight before (on any vehicle). My buddy with the ZRX 1100 has just had the 2nd one go out in the past couple years, and it got me looking into his options, and I realize I don't understand headlamp parts numbers. I see numbers like 9001 and H4 and H7 and 9003. But it looks like these are used in different combinations. Obviously there are tons of cars and motorcycles out there, and most likely they are sharing a pool of common lamps.
So can someone just sort of summarize how this works? Are all H4s (for example) interchangable, whether they are on a Jeep or a motorcycle, and then it's just a matter of which brand or model you want (that is, do you want a Philips, or a halogen, or a xenon, etc.?)