Looking to install a brighter bulb.
Not sure how bright you want to go....bulbs with much higher than normal wattage require the use of a relay, to keep from burning up switches and wiring. If you would like a slight stepup without the need for relays, I'd suggest a Osram Ralleye bilux H4, a 70/65 watt bulb #64205. It is a Halogen bulb with great light output. I have run all the way up to 130/90 wattage bulbs before, but the 70/65 watt seems the best for me. Try:
http://store.candlepower.com/numerical-listing-click-to-continue.html48911
NARVA H 4 12V 100/55W P43T
48901
NARVA H 4 12V 100/90W P43T
48951
NARVA H 4 12V 130/100W P43T
64205
H4 12V 70/65W P43t HALOGEN
64206
H4 12V 85/80W P43t HALOGEN
All these will work, remember that they are not "LEGAL" for on road use, so don't brag about them to an officer!
To me better lighting always wins out. The 70/65 won't blind the oncoming drivers like those 100, 130 watt bulbs can.
Good luck!
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