1977 Yamaha RD400

Q: I can’t seem to get electric power to my RD. When I turn the key I get no red or green light on the dash. This started after I hooked a charger to the battery. The battery is good and I have replaced the four glass fuses of the right side under the plastic panel. There is a square silver electrical part that may be a regulator. Perhaps this is bad? Are there any other hidden fuses or inline fuses on this bike? Any ideas would be helpful — especially where to get parts, oh and this is a US bike.

A: It does seem to be significant that the problem only started after you connected the charger, which presumably was a large one for a car and I imagine you did not disconnect the battery leads. It is therefore likely that a component has been damaged by excess voltage, the most likely candidates being the rectifier or the regulator. Having ensured that the four fuses in the fuse box (these are the only ones fitted) are okay, look for those two components and separate the multipin connectors. The rectifier has five wires, three of which are white and the others are red and black. The regulator has three wires: brown, green and black. Without starting the engine, switch on the ignition and check if the display is normal and the other components (lights, horn, etc.) work. If so, one of the two components is at fault.