QuestionI have an '82 VF750S (V45 Sabre) that I purchased not running. It had sat for at least 3 years and was reported to have an electrical problem in the instrument cluster (reported as "smoking", which was definitely the case and was fixed with a new varistor on the warning unit circuit board). After rebuilding the carbs and getting it started, I realized one of the CDI igniters was also out (repaired using a new zener diode). The headlight was burnt out, along with one of the tail lights. Now, after getting what I thought was everything electrical fixed, I took it out for its initial ride and blew another headlight within minutes. I then checked the voltage at the battery and found that at high revs, the voltage increases to about 17.5VDC, suggesting to me the regulator is toast. I bought a used replacement, but upon installing it, I still have the high voltage problem. Being that both regulators demonstrate the same symptoms, I wanted to check with someone knowledgeable in motorcycle electrical problems before I buy another one (a new one this time) to assure I am not missing some other charging system failure that might also create this problem. Any help will be greatly appreciated.
AnswerSometimes excessive voltge is caused by resistance between the green wire to the regultor/rectifier unit and the negative terminal of the battery. The regulator can only regulate the voltage between it's + and - terminals. If there is resistance between the regulator's - and ground the voltage dropped cross the resistance will be added t the regulated voltage.
You could go through all of the green wire connections in the harness between the reg/rec and ground and all of the mechnical connections between where the harness connects to ground and where the battery - connects to ground, but it's usually easier to splice an extra wire to the reg/rec's green wire and run it directly to battery negative.
BTW: The excessively high voltage could be the entire cause of all of the other problems.
MORE ADDED;
I've been thinking about this. Most bikes (including yours) have alternators that consist of a rotor (the engine's flywheel with permanent magnets mounted in it) and a stator (fixed coils that surround the rotor). When the rotor rotates the fields of the magnets move through the coils and generate electricity. Since the magnets always have the same field strength, the stator's output is always the same for a given RPM. The output voltage is regulated by shunting the excess to ground with a zener diode in the regulator/rectifier. The regulator can only control what happens between it's own terminals so any resistance between them and the battery will cause higher voltage across the battery.
I'd start by measuring the voltage between the green wires and the red/white wires at the reg/rec connector.(BTW: make sure that both red/whites are connected together and both greens are connected together.) This will tell you whether the regulator is regulating the voltage to the level it should be - if it is in the 14-15V range the regulator is good.
If the regulator voltage is OK, the next step would be measuring the voltage between the battery's negative terminal and the reg/rec's green wire (the meter's black lead should go to the green wire). If the wire you added is connected properly and is heavy enough (it should be at least as heavy as the bike's wiring) there should be no voltage. If you find any voltage at all you need to check that wire and it's connectons.
If there is no voltage there, the next thing to do is measure the voltage between the red/white and the battery's positive terminal (the meter's red lead should go to the red/white). This should also be zero. Unfortunately, if your problem is there you can't just put in a jumper like you did in the negative circuit. You will need to consult a wiring drawing and start measuring between the red/white and each point between there and the battery +. The problem will be wherever you find voltage between places that should be connected together.
