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Wiring the "Low-Beam Only" H4 HID kit
System Category: Electrical
Activity Type: Modification
FJR Model Year: 2003  2004  2004 ABS  All model years
Date Submitted:November, 2005

Wiring the "Low-Beam Only" H4 HID kit

So you can use stock headlight switch!

The H4 "Low-Beam Only" HID Conversion Kit featuring the McCulloch G5 ballast.


For the FJR pilot who has auxiliary lamps installed on the bike, there are several key advantages to selecting the "Low-Beam Only" H4 HID system over the "Hi-Beam/Lo-Beam" version of the H4 HID kit:

  • The "Low-Beam Only" save over $100 in cost over the Hi/Lo-beam version of the kit.
  • The Low-beam version can be wired as two independent circuits for the sake of redundancy. Should anything happen to one lamp, the other is unaffected.
  • The Hi-Beam on the "HI/Lo-beam" kit is truly overwhelming in the presence of other traffic. If you primarily ride in metro areas, you simply can't use the high-beam anyway without being socially irresponsible... and attracting undesired LEO attention.
  • Connecting the Lo-Beam only system is ridiculously easy... as seen in the photo above, it's white to positive, black to negative, connect the blue and red Murphy-proof HID capsule connectors, and you're done!

In this scenario (using "Low-Beam Only" HID lamps), one would ideally want to have auxiliary lamps (such as the PHIDs, or Hella's, PIAA 910s, etc) installed on the bike and let them function as high-beams when out riding (um... riding alone with no prevailing traffic!) It follows, then, that one could simply connect the stock low-beam connector to the "Low-Beam Only" HIDs, and use the stock high-beam connector as the signal wire to the relay firing off your auxiliary lamps. Again, there are significant advantages using the bike stock headlamp circuits:
  • Unlike most other motorcycles, on the FJR, power doesn't flow to the stock headlamp circuits when you switch the ignition on; it is only after the engine is started that the headlamps engage. This is PERFECT for the HID system, as otherwise, the HIDs would ignite when the ignition is switched on, extinguish when the starter button is engaged, and then have to re-ignite a second time after the motor fires. It would be preferred if we could avoid this second ignition sequence.
  • Lighting off the HID capsules does consume a good bit of electrical power, and one generally wants every bit of spare power available to spin the starter... and light off the headlamps afterward.
  • Come time to light off your aux lamps, you simply use the normal, thumb-operated switch to engage them.... no more taking your hand off the left grip and fumbling around for a toggle switch.

The H4 "Low-Beam Only" HID capsule, heavily shielded to prevent "scatter" and glare to oncoming traffic.

The Problem:

All this is well and good and sounds very attractive, but it's immediately apparent that this is a flawed approach. Remember, we are dealing with a dual-filament H4 system here, so what happens to your "Low-Beam Only" HID lamps when your thumb hits the switch to High-beam? Yep, you got it... the HIDs extinguish, since the stock low-beam circuit de-energizes when it's switched to high-beam! Obviously, this is no good.

One could solve this problem by simply taking the left stock headlight connector, wire the low-beam and high-beam circuits together, and wire your HIDs to the resulting circuit, and then it wouldn't matter if low or high-beams were engaged, power would always flow to the HIDs. Then use the right (stock) high-beam connector as the signal wire to the aux lamp's relay.

But now you created another problem, one that is even worse!

Since the factory wiring has the two headlamp circuits connected together, if you apply power to the left hi-beam circuit, power travels "back" through the stock wire harness and reaches the right high-beam connector... which you're using as the aux lamp signal! Now your aux lights fire off regardless of stock headlight switch setting!

Obviously, this is no good either. What to do?

The Solution:

Most fortunately, a simple, common 70-cent diode solves all problems! A diode is nothing more that a one-way "check valve" for electricity. Power flows unhindered in one direction as it always did. However, electricity can not flow "back" the other way... which is EXACTLY what we want in this application! The (stock) left headlight connector can be wired as shown below, and the high-beam wire on the (stock) right headlight connector can serve as the signal wire to the aux lamp relay:
Wired as shown, there will always be power to the "Low-Beam Only" HID relay as long as the engine is running. It matters not what position the stock headlight switch is set to; the Lo-Beam Only HID lamps are always lit regardless because the left headlight connector will always be sending a 12v signal to the HID relay.

However, when the stock headlight switch is set to "High-beam", the right headlight connector (which is serving as the signal wire to the aux light relay) fires off its 12v signal, and thus fires off the aux lamps. Now you have the very best of both worlds... HID low-beams on at all times, and your Aux Lights (acting as your "hi-beams") lighting off only when you thumb the stock headlight switch to "high".

Now you can go out and OWN THE NIGHT!

*** NOTE!! NOTE!! NOTE!! NOTE!! NOTE!! ***

The above schematic ASSumes you are using the headlight connectors as the positive (+) signal only to the RELAYS that are actually powering your "Low-Beam Only" HIDs and aux lamps!! If you desire to use the stock headlight connectors to power the HID ballasts themselves (and there is no reason why you can't), you need a heavier-duty diode... I wouldn't use anything less than a 10-amp diode for that application.


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