The wiring and fuses should have no problem with an 85 watt headlight. I'm running TWO 85 watt headlights on the stock wiring and stock 15 amp fuse. No smoke yet!
You didn't exactly ask about this, but here's another piece of the pie. Can the generator/alternator handle the extra wattage of an 85 watt bulb (compared to the stock 65 watt bulb)? My service manual indicates the generator/regulator can provide 22 amps @ 1200 rpm, and 36 amps @ 3500 rpm. If we assume the low rpm case, and lets say 13 volts, we get (22 amps) x (13 volts) = 286 watts. At the higher 3600 rpm we get 468 watts. Ok, that alone is plenty for an 85 watt bulb, but first we must subtract for the tail/running lights, ECM/TSSM/IM/Spark/FuelPump, and two radiator fans. My quick check suggests the fans may be as high as 85 watts each (ouch). The tail/running lights should be less than 30 watts total (don't stand on the brake, and run the turn signals all day), and the ECM/TSSM/... is under 1 watt (mine measures 0.87 watts when the fuel pump is running). So if this is correct, we have:
85 watts (fan 1)
85 watts (fan 2)
30 watts (tail/running lights)
1 watt (ECM/TSSM/...)
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= 201 watts (without headlight)
Now, if we add an 85 watt headlight (assuming high and low beams are not on at the same time), we get 201+85=286 watts. Oops, we are exactly at the 286 watt limit if the engine is idling, and the fans are running (without brake light and turn signal). BUT, we are well under the 468 watts if the engine is at or above the 3600rpm point (riding). Now, I'm probably a bit high on the fans, so in reality, it's probably fine even at idle. And, I'm guessing you would be in quite a unique situation if you leave your bike idling for a LONG time (tens of minutes or hours), and the fans are running the whole time (VERY hot day). So, I would assume (based on these calculations) that the generator/regulator can easily handle an 85 watt headlight.
The "real" HID lights consume far less power (half or better) than standard bulbs, so they would improve the power margin even though they produce more light.
My bike has
FOUR fans, and
TWO 85 watt headlights. So far I have had no problems. But then again, like Kaz, I don't sit around idling much!
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