After searching through the forums and finding almost no concrete information, I've decided to post the results of my research and hopefully save other TT members from repeating my mistakes or wasting time looking through multiple posts for bits of information. This post outlines instructions (with supporting explanations) for adding a battery and aftermarket regulator/rectifier to a 2002 WR426F (US model) WITHOUT modification of the OEM stator. A PDF of the electrical wiring diagram for the 2002 WR426F can be downloaded from http://www.wiringdiagrams21.com/2002-yamaha-wr426f-and-wr400f-electrical-system/ (the PDF password is: wiringdiagrams21.com) and I found the best wiring diagram for the regulator/rectifier on Trail Tech’s web site at: http://www.trailtech.net/media/instructions/lights/regrec/010-ELV-71.pdf. The battery's negative terminal and all negative/ground returns must remain isolated from the frame and from the black stator output wire (this is called “floating” the ground). This means that the battery’s negative terminal and regulator/rectifier must be mounted in such a way that they do not contact the frame. The aftermarket regulator CANNOT be mounted in the same location as the OEM regulator (on the left side of the steering stem in front of the fuel tank), because this location attaches the aluminum frame of the regulator/rectifier directly to the steel frame of the motorcycle and ties it to the frame ground (which is receiving AC return voltage from the stator). I found the most suitable location for the regulator/rectifier to be inside the airbox (you may find a better spot), which mounts to plastic and isolates it from the frame. The OEM regulator simply limits the output voltage so that 12V components are not damaged (i.e. headlight, taillight, lamps, etc.), but still outputs AC voltage (in other words, it does NOT rectify the output to DC voltage). The current aftermarket regulator sold by either Baja Designs or Trail Tech has five wires which are connected in the following manner: For batteries with a capacity less than 4Ah: • Two YELLOW wires for input from the stator, connected to the single-pole output and frame ground ('98-'02 WR's). The output of the stator is one yellow wire under the tank on the right side of the frame (on mine) which led to the yellow switch power for the lighting circuit (see the electrical diagram) and one black wire which is under the tank on the left side in a wire loom (again on mine) and is ganged together with the common frame grounds for the lighting and ignition circuits. • The RED wire is connected to the positive terminal of the battery (usually red) and all positive connections for the load (headlight, taillight, lamps, etc.). • The BLUE wire is connected to the negative terminal of the battery. The blue wire is current limited to prevent over-charging of the battery, which will dramatically shorten the life of a small capacity battery. The blue wire WILL NOT power headlight, taillight, lamps, etc. If your headlight dims at RPM’s above 2500, check the connection of the blue/black wires. • The BLACK wire is connected to ALL negative returns from the load (headlight, taillight, lamps, etc.). This wire is NOT current limited and will allow all possible output from the stator, which is 120W (minus battery charge power) in the case of the 2002 WR426F. For batteries with a capacity of more than 4Ah: • The BLUE wire is NOT USED (this allows full charging capacity for larger batteries from the stator). • THE OTHER CONNECTIONS ARE THE SAME AS ABOVE. I used bullet disconnects for all of the connections except the battery (these were female spade disconnects). The bullet disconnects allow connections to existing wiring and allow for quick changes in configuration. I used spools of 16AWG stranded primary wire in various colors and I picked up the battery (1.3Ah sealed lead-acid) at Batteries Plus. The cost of this project was ~$60 and the only part I had to order was the regulator/rectifier (which I got from a fellow TT member). Please feel free to PM or e-mail (firstname.lastname@example.org) with any questions regarding the above information.