I own a Royal Enfield Bullet (std) 350cc 2013 uce model. The bike is fitted with a 35/35w HS1 PX43t halogen bulb. I want to replace it with a 60/55w halogen H4 bulb.

Earlier I had installed the self start motor on the bike so the battery has also been changed from 5Ah to 14Ah.

Do I need to install a relay, or rectifier and new wires? Will the H4 bulb fit in the existing holder? What are the other things I need to consider before installation? So that no harm is done to battery or electrical system.

  • You may also want to look at an HID upgrade kit, although that requires putting additional electronics, HID uses less amperage and are brighter for a given wattage. The kits are now quite inexpensive and reliable. I've been using DDM on several of my bikes and haven't had any problems.
    – Paul
    Sep 25 '14 at 0:12

This thread on a motorbike forum suggests that an H4 bulb will fit in an HS1 holder, but that the bike in their question has a plastic lens that could melt - yours may be the same?

Does the alternator have enough power to run the higher-wattage bulb and recharge the battery?

I would always use a relay when upgrading or adding lamps, Halogens work much better when they have the full voltage and current available to them, and using a relay and good quality suitably rated wiring reduced the losses involved. Always use a fuse as well!

  • 1
    So everyone knows, the difference in amperage between the two bulbs is ~2.1A (35w v 60w). Sep 15 '14 at 21:51

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