Topic: Wiring monkey messo - how to fix

[mycb750k6]

I recently bought a nice 71 CB750 but when I opened the seat I found this mess (see picture). Maybe this was a saddlebag setup or Mack truck tail light array or whatever but I have a drain somewhere and it's likely in this mess. I'm going to start cleaning each connector today but I'd like this mess outa there if I can. Any suggestions. I don't see any new K1 wiring harnesses on ebay.

[HondaMan]

Well, there isn't a lot of wiring in a K1: a "leak" is almost always a damaged rectifier. Unplug the rectifier and charge the battery, then let is sit overnight and see if the battery stays up. If not, the battery is bad: if so, replace the rectifier. On the K0/K1 bikes, the rectifier was only 20 PIV rating, and hitting it with a 10 amp battery charger is enough to damage them. The newer rectifiers are 50 PIV and can withstand a 10 amp charger.

Always use a 6 amp charger max on these bikes, for this reason...2 amps is better... 

In that area, there will be a YELLOW/RED wire that comes from the electric start button and goes to the starter solenoid. The other end of that solenoid is tied to the BLACK wire circuit in the main harness. There will be a BLACK, a WHITE, and a GREEN wire on the voltage regulator, and the regulator has a label on the side that shows where these connect. There must be a GREEN wire from the harness that has a ring terminal on it, and this goes to a 6mm bolt near the seat latch: this MUST be connected there or little else will work. There will be the big 6-blade plug to the rectifier, a BLACK and GRAY wire to the little flasher module at the back of the battery case (early K1 may have a color other than GRAY for the second wire there), and the big 8-blade plug to the alternator. Three of the yellow wires in this big plug go to the rectifier's plug: a GREEN/RED wire from this plug goes to the NEUTRAL light, a WHITE and BLACK from the voltage regulator goes to the field coil in the alternaotr, and the last wire goes to the oil pressure switch (color escapes me at the moment). That's the sum total of the wiring here on a K1.

[mycb750k6]

Thanks Hondaman. I'll try the disconnected rectifier test first. Will a newer, higher rated, rectifier work on the old K1 or will I need to get the correct part if I find that it's bad?
I use a 750 mA charger which takes overnight and then some to fully charge but I'm in no hurry. I will say the battery comes to full charge after an overnight charge but after a day of sitting, the charger takes about an hour or two to re-charge. After three days of sitting it takes two-three hours. Longer than that and it takes an overnight charge again. The bike is still in some state of dis-assembly so I am unable to start it up again just yet but before I pulled it apart it ran fine so I believe this electrical problem has been there since I bought it.

[srook]

I got my brand new OEM wiring harnes for my K1 from David Silver.  It wasn't cheap but they are still out there.
Scott

[Bodi]

A rectifier is a rectifier - getting the Honda one will get you the exact connector and avoid any hassles there. However, there are quite a few aftermarket ones and you can use an industrial standard 3 phase rectifier bridge block, or two single phase bridge blocks. The wiring is pretty simple to figure out if you decide on a non-OEM type.
The rated voltage issue is important, rectifiers are rated for maximum current (25A should be plenty) and PRV, peak reverse voltage: this is essentially the maximum voltage it will handle. Although the bike is a 12V system, the actual peak reverse voltage at the rectifier will be higher. Using a battery charger can give quite a bit higher voltage, a 20A charger will put as much voltage as it can to try and get 20A flowing. As a rule do not use anything more than a 2A charger for these little batteries, 5A will be OK if that's all you can find in an emergency but if you buy a charger for the bike get 2A max and an automatic "battery tender" bike battery charger is much recommended.
As for the wiring, HM is right that the wiring is pretty simple on a K1, only one fuse and much simpler circuitry than the later multi-fuse models. I can't imagine what your terminal strip (definitely not original!) was added for, you would have to trace the wires to figure it out. If there are original wires attached you can determine what they are by colour, using a Honda owners manual or shop manual wiring diagram, you should be able to find one online for download. Avoid the Clymer and Haynes wiring diagram, they skip stuff and simplify stuff: danged annoying to try and figure out a harness when the diagram is not complete. A diagram for a later model with three fuses will make you nuts, although the basic wire colours are the same basic functions the ignition switch and fuse wiring is complicated and just confusing if your bike is a single fuse model.

[mycb750k6]

Thanks Bodi. You sound like you know what you're talking about too. I went through the wiring nightmare on my 76 and with the help of a few folks here got it all sorted out so if the K1 is simpler, I'll dig in. I just don't care for electrical stuff but like everything else it's pretty satisfying when you finally figure it out.