I just discovered the source of my confusion; nothing like actually doing the job. I thought the rubber boot over the connector was a separate piece from the large round cover, which I thought was plastic. Turns out it is just one big rubber boot. Thanks for your help...
Originally Posted by Paul_F
Yeah, I probably would too.
Originally Posted by bobr9
I created this spreadsheet to illustrate the benefits to be had by upgrading the headlight wiring in my BMW R1100RT.
This motorcycle has a single standard 55/60 H4 headlight bulb, with 18 gauge wiring. The current to power the bulb goes through the low/high switch on the left-hand handlebar. The total run length of the wire is probably 6 or 8 feet.
There are two parts to the sheet.
The main part to the left shows various intermediate values and formulas leading to the %Brightness column.
The light blue box is a shortcut version displaying brightness for a given wire size for different wattage bulbs.
When engineers design wiring they usually try to keep the voltage drop (and thus the power loss) to less than 5%. As you can see the stock wiring falls well below this at 2% drop with the stock bulb on high beam.
Because of the way light bulbs work, a small voltage drop can result in a significant loss in light output.
With stock wiring the stock bulb is running at about 99% of its rated brightness on high beam. This seems acceptable.
But over in the blue box, watch what happens when we try to get more light output by moving to a Philips X-treme 80/100 H4 bulb.
The X-treme claims to produce 80% more light than a standard bulb. However the increased current flow increases the voltage drop and thus diminishes the light output of the bulb. The new bulb will still be noticeably brighter than stock, but instead of being 80% brighter, it will be (92% of 180) - 100, or about 65% brighter than stock.
Moving to 12 gauge wiring and relays brings the light output of the hotter bulb back up to the where it should be.
Also keep in mind that power isn't really lost, it always goes somewhere. Any power that isn't getting to the light bulb is being used to heat up the wires.
Instead of buying and installing a kit, I run a Sylvania Silverstar bulb. It is still 55/60W, but is quite a bit brighter and whiter than the stock bulb. It is NOT 80% brighter, more like 25%. And if you do this you will want to carry a spare Silverstar, and possibly a spare OEM el cheapo bulb. Why? The stock bulb is extremely tough. A conventional H4 bulb might last 10 years or 20 years, but you can count on the Silverstar burning out within a year or two. Sylvania does not boast about the short life expectancy of course but they also don't make it any big secret. I don't know if the X-treme has a short life expectancy as well - I would say probably.
There's no magic there. Incandescent bulbs make light by heating a piece of wire to incandescence, which is, dang hot. The hotter that wire gets, the more light comes away from it. The hotter the wire gets, the shorter the amount of time it will survive. The Silverstar uses a time-honored trick of being "designed" for a lower voltage than it will actually be run at. Before we had fluorescent bulb replacements, you could find "140V" light bulbs for the house, which would run cooler and last longer when run at the actual house voltage of 120V.
Last edited by scott.lambert; 05-11-2013 at 10:15 PM.