Headlight Relays

[Flying Duck]

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/ ... _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__Pro ... ctors.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:

[skdonlan]

Wow, I didn't know what I didn't know, and kind of wish I still didn't know!

One more item to add to the "gotta get list".

Those prices seem very reasonable, for what you get out of it.

My head is spinning trying to figure which kit would be best, need to read it again.

Thanks for a great write-up Duck. This ought to be a sticky!

[Flying Duck]

Jim has owned a few Ks. Drop him an email and ask him which kit - then please report back on this thread.

You can tell him you were referred by a duck. Jim knows who I am. I've ridden with him before:



He's a tall guy - he made that K100RS look like a minibike when he was riding.

[skdonlan]

I went back and re-read the kit options and it seemd like this one would be best. We don't have dual beam headlights do we?

H4 Heavy Duty Single Headlight Relay Kits with Ceramic H4 Socket

I went ahead and ordered it with two additional posi-taps as per your reccomendation.

Thanks for another great lead on an improvement for our bikes.

Now I'm going to contemplate those Catz....

[Flying Duck]

You don't need the Posi-Taps with Jim's kits. In your case the non-cermaic connector plugs into your old headlight socket to trigger the relays. That's part of what makes Jim's kits so easy to install.

But keep those Posi-Taps around - they'll come in handy some day.

[skdonlan]

You're right, he said he now includes two posi-lock connectors so that you don't have to use the socket connecter, which is apparently rather bulky(?). But you can go either way. He also said I ordered the correct kit for our bikes. (The ceramic plug is a slight upgrade, not neccesary, but it was only a few bucks more and all that reading about bulb heat had me concerned)

He's got a great website, very infomative for the non-electrically inclined, a good read if you're curious about better lighting.

[Scott_Anderson]

I was a little disapointed earlier this year when I wanted to order the headlight relay kit with the modulator. Only to find out that he's not selling the Diamond star modulators anymore.
He told me that he's working on a new style modulator but it's not ready yet, and he was having problems with diamond star so he quit using them.
I ordered the diamond star unit direct so I could have the same setup for both bikes, and the basic headlight relay kit from Jim.

[Jim]

Scott - why did you order the Diamond Star if they have issues? Kisan makes a perfectly good headlight modulator - plug & play.

[Scott_Anderson]

In my e-mails with Jim, it appeared that his issues were with the company, not the product.
I have been totaly satisfied with the product on the '97 so I wanted another for the '95.