Headlight Relays

[frankenduck]

Lots of people add headlight relays to their K bikes. Why?

1) The stock wiring for BMW headlights is rather wimpy.  It suffices but given the small gauge of the wire, voltage is lost in the circuit.  By upgrading to thicker wire (like 14 gauge or even 12) the amount of voltage lost is much less.  More voltage to your headlight means more light.

2) Since, from the factory, the headlight does not use relays this means that all of the current travels through the contacts in the high beam/low beam switch on your left handlebar.  Every time you switch between beams a little spark is created.  Over time and many uses, these little sparks degrade the switch contacts and eventually cause the switch to fail.  When you use relays, the current flowing through the switch is reduced to next to nothing and this increases the longevity of your headlight switch.

3) Once you've upgraded the wiring and added relays you can switch to a higher power bulb.  If you tried that with the stock wiring chances are you'd melt the insulation off of the wires and have some potentially serious problems.  (I run a 90/100W Xenon H4 headlight bulb which is a massive improvment over the stock halogen H4 bulb.)

You have two options when adding headlight relays:

1) Buy a kit from Jim Davis at Eastern Beaver.  If you're not into chasing electrons or just don't feel like making your own, Jim's kits are handy, fairly priced and used by lots of K bike owners.

Jim's page of H4 headlight relays:
http://easternbeaver.com/Main/Products/H4_Kits/h4_kits.html


2) "Roll your own"

You can find a couple of write-ups on this over at the IBMWR K Bike Tech Pages:

http://www.ibmwr.org/ktech.shtml

You can  either use your existing headlight plug and cut the wires very close to the headlight socket or you can get a new H4 headlight socket and connect your higher gauge wiring to the socket. This is really the "right" way to do things. (I get mine from Jim Davis - http://easternbeaver.com/Main/Elec__Products/Connectors/Headlight_Connectors/headlight_connectors.html )

I'd also recommend using Posi-Taps to tap into the headlight wires from your switch.  Jim Davis has those too.  You'll need two of the PT1800 type.  (I do not recommend using ScotchLocks or T-taps - both have a tendency to fail or cut through the wire you're tapping into.)

Here's a quick and dirty hand drawn wiring diagram for adding headlight relays.

Oh, and be sure to disconnect your battery before doing stuff like this.  (Have your radio security code handy if you have an LT.)


EDIT:  Here's a better wiring diagram.  Note that the wires indicated by thicker lines are the ones where you should use 12 or 14 gauge wiring:

[oldfieldcycles]

i am thinking about ordering the eastern beaver headlight relay for my RS. im wondering if i should wire it directly to my battery or should i wire to the fusebox?

[Scott_]

The kit will come with terminals to connect to the battery and the harness will have a fuse holder. (or at least they used to)

[billday]

Got one last winter: yes, it wires to your battery, there is an inline fuse.

[oldfieldcycles]

he offers the harness with or without an inline fuse. without he suggests wiring into your fusebox if you have any extra space in there. the RS has space for more fuses, would it be difficult to do this? i think it would be a cleaner wiring setup.

[Scott_]

There may be empty fuse sockets in the housing, but they are not wired.
I've not tried to put terminals in the empty sockets, Drake has tried and found it actually easier to add a separate fuse block beside the stock one.
He posted a write up on adding the fuse block but the pictures are gone and we haven't been able to find them yet.

Edit
Here's the link with the photo's replaced.
http://www.motobrick.com/index.php?topic=1148.msg4816#msg4816

Thanks RBM for the search tip of using the *, I've been trying google search for the missing pics but it hadn't been working well without the wildcard....It still took some digging but I was able to recover them. :2thumbup:

[rbm]

Look at "Add A Fuse" on this page:
http://www.kbikeparts.com/otherstuff/otherstuff.htm
Duck sells salvaged connectors with pigtails that can be added to an existing fuse block.  There is a plastic retainer that can be removed.  The connectors are inserted into the spare locations and the retainer replaced, then the pigtails are wired up.  For images, look to Google for images which contain addafuse*jpg and k75f_auxfuse*jpg in the name.