Topic: Charging system fuse location?

[jerrybb]

I'm having charging problems on my CB750-K4 and after a lot of checking, I don't think there is power going to the alternator. A fuse is shown in the schematics that feeds the charging system, is it hidden somewhere, like under the tank? Or is it one of the three on the fuse block? I haven't checked the terminals from the ignition switch yet-just recently got the bike and found it was not charging. After pressure washing and playing around a bit it started charging 14.5v and I thought I was home free. Now it's dead again, so I'm thinking I have a bad connection to the system. I cleaned all other connectors from rectifier, regulator, etc. Thanks,  Jerry

[Jerry Rxman Griffin aka MuthaF'er]

Did you check the connectors from the stator located behind the side cover? I don't think there are seperate fuses in addition to the fuse block (at least not on a F). A blown fuse is a blown fuse. Be glad you found 14.5V! If it were me, I'd go through each and every connection, clean them, and apply dielectric grease to keep any moisture and corrosion away and be done with it. So many of these bikes have charging issues.

Jerry also

[kettlesd]

yeah - what RxmanGriff said.

I stopped chasing poor connections when problems come up years ago. Now when i get a new toy, I go over the electrical front to back and be done with it.

[jerrybb]

Yes, I did check the leads from the stator behind the lower cover but all I did was unplug and replug all of them (looked pretty clean) but did not clean them all. Still could be a bad joint on those wires or another. The fact that I did get 14.5v for a while is reassuring but I ain't getting it now for sure.  Whoever said "They don't make them like they used to" was right.  They're a lot more trouble free now, but of course I don't know how my Toyota will be in 33 years-prob not as good.

[Bodi]

Take a look at the wiring in a new bike and you won't be so hard on yours. There's probably 20 times as many wires now, and a troubleshooting mistake can mean a $500.00 ECU computer is fried.
The wiring is pretty simple and worked well when new... this is a good clue that it needs some "renewing". The wire doesn't usually go bad (occasionally the flexing section around the steering stem does fail) so what's left is the connections and switches: the exposed metal corrodes resulting in poor and intermittent contact. Kettlesd said it all - you can chase elusive and occasional electrical glitches forever or spend a few hours cleaning all the bullet connectors and the multipin spade connector terminals, tightening the females and adding some dielectric grease to seal out air and moisture. After that you may still have problems but they're likely to be component failures - regulator, solenoid, switches - rather than mystery wiring harness gremlins.

[TwoTired]

I don't have a K4 750.  But, I do have the shop manual schematics.  The only fuses are Main, headlight, and tail light, located together in a block.

The alternator gets power from the regulator via the white wire.  The regulator gets power from the bike via the black wires, which is the 12v distribution from the ign switch.  If you are only losing regulator or alternator field power and not the rest of the bike, then it is unlikely to be a fuse issue.

Do check the voltage routing with a meter.  But, don't ignore the voltage returns (green wires).  A break in supply or return will cause circuit failure.

With the ignition switch on, that white wire to the alternator should have battery potential on it.  If it doesn't, or has a lesser value, then you've got a dodgy bit it the path, to track down.  It's not that hard to do really.  If you can follow a road with a map, you can follow and electrical path with a schematic.  Some people just hate doing it because they think riding the bike is more fun.

Cheers,

[jerrybb]

Well, I have power going to the regulator, so there apparently is no problem with the ignition sw or wiring back to the reg. My testing of the rectifier, with my limited knowledge  but looked thru most of the dozens of rectifier pages here, indicates a bad one. After reading all the stuff I don't want to wait around to buy one from Dennis Kirk or other sources, and I for sure don't want to buy an OEM unit, so I'm going to build one from the specs given here. I already have two of the Radio Shack 25a-50v bridge rectifiers that I bought for my Trail 90's, so I'll wire them together per the diagrams others have given, and see what it does. No large amount of time or money wasted in any event. Film at 11.....

[jerrybb]

OK, finally got it charging properly. Testing showed that the rectifier was not really very good, so I built one using two Radio Shack units and a piece of aluminum for a box. Tested out properly but still no charging! Pulled all the connectors apart for the third time except this time I took the Dremel and cleaned every contact I could get to. I think the problem was with one of the terminals on the connector from the alternator. After putting it all back together I'm getting 14.5 at full charge. A nice feeling of accomplishment and learned a lot from this experience, thanks to all the posts here about troubleshooting. Total cost for the new rectifier about $8. 

[Jerry Rxman Griffin aka MuthaF'er]

How about a picture of that homemade rectifier?

[jerrybb]

I posted a photo of the setup tonight under "Homemade rectifier" file. Good luck