XJ750 charging system

ive recently replaced the fusebox and i used a slightly larger guage wire. did this lower the amps? the bike was in a minor accident with po and wires from stator got crushed and shorted against the cover, the red light was on. ive since replaced with all new, the battery, fusebox, stator coil, brushes, cover, cleaned the rotor contact surface and replaced the rectifier with a good used one but still the warning light stays on and i cannot ride the bike long before it starts cutting out and eventually dies. running a jump box to turn on when it starts to do that helps me get enough distance to fine tune the carbs it was fouling plugs badly after rebuild. the bike had not been riden after the wreck and sat for well over 10 years when i bought it. it had very low mikes from sitting so long but the speedometer was damaged in crash and had to replace it. it has less than 5000 miles on it and its a 82!

 

larger wire is good has higher current carrying capacity.
when bike is running what voltage do you get at idle 2k rpm and 3 k rpm?
go to bottom of this link and it has a good explanation of the system and charging issues.
The Ultimate Relay, Switch, Sensor, and Diodes Guide

you will want to test the output in AC for the stator.
and of course a new battery can be bad.

 

Thank you for responding. i have 3 new batteries it does the same. the voltage does not change when its running it starts at 12.9ish and slowly starts to drop at all rpms. that and the red light stays on is how i know its not working

 

The XJ's don't have a red light for charging. The bikes with the Atari Units do have a battery monitor that only indicates if battery fluid level is OK, or if modified indicates if battery voltage is somewhat OK. In either case the warning indicator is not a direct indication of not charging.

Did you read the link as XJ550H suggested? I suspect not or you would have failed along the way and would be asking a more specific question. Since you seemed to have all new / used replacement parts you have either installed a defective unit or you have an interconnecting wiring issue. Try to work through the guide in the link and see where that leads you.

 

OK, so, the alternator works by feeding DC to the field coil through the regulator. The regulator monitors the output, and reduces the field current to regulate the output at about 14V or a bit lower.

The output is from three stator windings. These feed into the rectifier part of the rectifier/regulator. The raw output is AC. The rectifier converts this to DC.

So, lots of things could be bad.

I would disconnect the plug between the alternator and rectifier/regulator and, first, check that the contacts in the plug are OK. There's a lot of current going through that plug, and dirty/corroded contacts will tend to burn up.

Assuming the plug is OK. Check that you have reasonable low resistance (a few Ohms, I'd guess) between the two pins that go to the field winding in the rotor. If you don't, then it could be a bad rotor, bad slip ring/plate, bad brushes, or broken wires.

Also check for the same, very low, resistance between each combination of two white wires (the stator windings), and check that there's very high resistance between these three white wires and chassis.

If all of that checks out, you probably have a bad rectifier/regulator. You can check what voltage you have going to the field winding when it's been reconnected. Should be pretty much the full battery voltage.