Voltage Regulator (again!)


XS400 Member
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Québec, Canada
My 1981 XS400 had run perfectly lately but, yesterday, when I turned the key, there was nothing; no lights no power to the starter. I checked the fuses, no problem there. I checked the battery and it was showing 12,45V. SO I figured that I must have a short circuit somewhere to have all the electricity moving to the ground instead of going to all the parts. I unplugged everything and started to check when the voltage at the battery would drop when a plug would be reconnected. I am now with the voltage regulator (the green wire to the alternator is already plugged) and the voltage dropped immediately and continued to drop under 12V until I unplugged it. I see 2 possibilities: 1- the brown (voltage reference) connection in the voltage regulator is now grounded (while there should be infinite resistance between the two in order for the comparator to have a voltage to compare to) or 2- the green (regulation) connection does not have anymore restriction in the regulator. Am I correct in my assumptions?
I have disconneted the plug that goes to the oil switch (Y), the neutral switch (L), to the field of the alternator (B) and back to the voltage regulator (G) and found that I could replug the regulator without any loss of voltage; this means that the problem is coming on the engine side of the disconnected plug. So I checked for anything that would be grounded on this side and found that the oil switch is effectively grounded. When I look on the diagram, this switch seems to be normally closed (letting the current go by) while the neutral switch is shown as opened (not letting the current flow). Is that really the case?
This is correct. For the oil switch to light the oil light at ignition on but not running, it is grounded. Once oil pressure is sufficient, the circuit opens, thus turning off the oil light. The neutral will only close the circuit when the transmission is in neutral and all other gears is open. I'd check the wires for the field coil and stator under the side cover. The insulation is known to harden and crack from heat and cause a short.
ok thanks. By looking at the diagram, I could figure that putting the gearbox in neutral would put this switch to ground so the other one had to be in the same state for the safety relay to do its job.
I now have electricity everywhere; when I turn the key, all the needed lights show their color! But the starter solenoid does not work. I have to find why. I will check tomorrow!
One thing though, I still have the battery being drained by the regulator / field wiring when both are connected to the circuit. As you say, I will have a look at the wiring under the cover.
This morning, I plugged directly the starter solenoid to the battery and this treatment has awaken it; I did not hear a small click but, instead, the thing made a BIG clock. Next step was insuring that, now, the solenoid really closes the bridge between the two terminals and, yes, it does. Then I connected the starter directly to the battery and it immediately turned. I then put back the starter solenoid in place and tried it with the little push button (newly directly grounded) and the starter made its usual music! Then, it was the alternator wiring that was to be looked at. One of the screws holding the side cover was really stuck so I used a propane torch to heat the cover (forcing it to expand) and the screw could be unscrewed. Before removing everything else around to see the condition of the wires inside the cover, I checked with my multimeter if there was any one creating a short; nope. So I simply put back the screws in place (with a little bit of rust inhibitor) and attached the + and - wires to the battery monitoring the voltage at the same time. The bad news is that I still see the voltage drop dramatically as soon as I connect it to the motorcycle, even before I turn the key. That leaves me with a short list of possibilities! If anybody has any ideas on what to look for, please let me know!
Ok! I checked the behavior of my car when put the key and when I turn it and that's the same behavior as on my motorcycle. So I put back the gas tank, plugged it and started the motorcycle while measuring the voltage of the battery. As soon as the engine ran, the voltage rose to more than 14V! So everything is fine now. I had a deffective battery and a starter solenoid which did not remember what was the meaning of its life! It made me find 'about to happen' problems that are corrected and clean the electrical contacts. So this thread is now complete and, hopefully, it will help somebody else!