Have been "planning" this installation for quite a while. Read a load of threads, asked a few questions and finally found someone who had actually made the install in an 1100GS and was willing to talk about it - Thanks Mike! Finally ponied up the $112 for an eBay slim ballast kit. The kit is for a car and comes with two ballasts, two lamps, but only one control "box". I'll be doing the install in the next couple of days and had a few thoughts to bounce around to those in the know. The wiring loom that comes with the kit is intended for plug-and-play installation in a car - taking power direct from a battery connection through a supplied fuse. It also combines the control functions for both lamps into one black box with an inscrutable diagram associated with it. I have deduced what it must do and plan to make my own harness, better suited to the GS. I am assuming the supplied harness does two things: Supplies power through a relay to the ballasts, switched on when either high or low beam is on Applies power to the capsule control to move the capsule when high beam is selected As the only opportunity to "sense" power comes from the H-4 plug, there must be a diode or two to allow voltage at either filament connector in the factory lamp socket to energize the relay. Also, I presume there needs to be a capacitor or other circuit to stop the relay unlatching momentarily if there is a power break for a fraction of a second while switching from high-to-low beam or vice-versa. Now, I'm not scared to get into the stock wiring and I would like something simpler and cleaner for the GS. Not to mention that I have to split the kit up so I can use half of it on my UK airhead RT. Therefore I have decided to re-wire everything. All that is required is to arrange for something to perform the two functions outlined above. Power for lights that can not be interrupted whenever the lights switch from high to low can come from the jumper installed by BMW to eliminate the lights on/off switch in US models. All I have to do is tap into that jumper wire. I am going to assume that the circuit is already capable of providing sufficient current to meet my needs and so will not bother with another (redundant) relay. Just to be sure, does anyone know exactly what the initial start-up current requirement might be? I expect it is quite a bit higher than the 3A that the 35W running power would suggest (I'll be measuring this for myself later by the way) The switching power for the high/low beam can come from the high beam circuit anywhere between the switch and the headlamp socket. I'll have a good look to work out the easiest place to tap into this but right inside the headlamp shell will probably work best, as that's where the power is needed. If I just tap into the power at the jumper than I still have an easy option to return the lighting to stock if something fails. Mike told me how to make sure the capsule fits in the headlamp. I'll take pics of that and any other "tricks" if necessary. If I get really enthusiastic, I'll also try to set up the requisite before/after shots. Anything I've missed?