The following electrical wiring diagram applies for 2003 KTM Engine 400 660LC4 models. Herein you will find brief information about charging system, leakage inspection procedures, charging and checking the voltage regulator, battery, capacitor, starter system, relay, idle switch and ignition system CDI unit, ignition coil and wiring diagram.
Checking the voltage regulator-rectifier: Start the engine and switch on the low beam. Connect a voltmeter to the two terminals of the capacitor (red/white cable = positive, brown cable = negative). Accelerate the engine to a speed of 5000 r.p.m. and read off the voltage. Nominal value: 14.0 – 15.0 V. If the reading significantly deviates from the nominal value above, check the capacitor. If the capacitor is intact, replace the voltage regulator-rectifier.
Find the detail of 2003 KTM Engine 400 660LC4 Electrical System Diagram here (121 pages of pdf file docs.)