I ran an H4 in a Cibie lens for as long as I had a 750 (long time). Stock no relay, but a relay would've helped I've learned since.
How would it have helped? I have an H2 bulb in a vintage lens...and I was told a relay would be necessary...just trying to sort that out.
No its not necessary as I and others can attest. Just install it and go. You will still get more light even without the relay. But if you do it, you'll like it even more.
All the current for the bulb goes thru the handlebar switch. Luckily, it can handle it, but you are stressing it. With the relay, the switch handles a much lower level of current, it turns on the relay which can then handle the higher draw of the bulb safely. Hence the light is much brighter.
I don't understand electricity other than to know what works and should be in concept. For instance the starter runs thru a relay for the same reason. The starter draws so much current if it didn't go thru the relay (solenoid) it would fry the handlebar switch the second you punched it.
After parking the 750 for il leaks I took to my 88 hawkGT. The guys at HawkGT.com were all gaga over relays. So i bot one from a guy that was kitting them out. Installed it and the stock headlight was a good 20% brighter.
Here's where i got the relays for my current project, horn (louder stock, or to drive bigger horns) and headlight.
http://easternbeaver.com/Main/Products/H4_Kits/h4_kits.htmlTrue it can be done "Do it Yourself" but I need the extra help a custom kit can provide.
Here's their FAQs, a little hard to find:
http://easternbeaver.com/Main/Stuff/Faqs/Relay_Info/relay_info.html