Any CT70 electrical guru's out there?

[Lex]

I'm restoring a K4 CT70 that somebody who had no idea what they were doing was working on. The problem I'm having is when I hook up the battery it drops to 4.2 volts. It has a new harness and a new key switch. The regulator/rectifier was getting real hot so I replaced it and it didn't change anything. Has anybody ever ran into this before I start unplugging each wire one by one and checking all the switches? Thanks!

 

[Enginedoctor]

It sounds like the rectifier might be shorted to ground. If its getting hot, likely current is flowing through it. If the battery drops so dramatically when connected, something is eating up the power, or essentially providing a path to ground, and one that draws a decent amount of amps as well.
If the last person didnt know what they were doing, maybe this is a good opportunity to either replace the harness or fix their shotty work.

With the battery out, you can test for resistance from the positive side to ground. Unplug suspects until the resistance increases to almost infinity....

 

[red69]

You misspelled shitty.

 

[Lex]

Enginedoctor, If you read in my post I already replaced the harness and the rectifier. Any other ideas? Thanks

 

[dirtbkr188]

You misspelled shitty.

....or, he may have misspelled shoddy...

 

[Enginedoctor]

Okay. Since therectifier has been replaced and still doesnt work, lets start there. I assume its properly gounded, so make sure the wires to it are hooked correctly. One should be green, and the one to the battery and ignition switch should be red/white. The only diagram i have for this bike is lackluster, at best.
When you replaced the harness, did you hook it up the same way as the last guy, or was it too butchered to even tell? Does the rectifier get hot no matter what or only when the bike is running? Have you tried switching the leads to the rectifier? The diode in there would prevent b+ from getting a path to ground.

 

[Enginedoctor]

Yeah and i misspelled shoddy. So shitty is a viable synonym.

 

[69ST]

With a turn signal-equipped bike that has an unknown history, plus obvious signs of ham-fisted, kludge, repairs this can seem overwhelmingly complex. IMHO, best to take it in small, manageable, steps. The one thing that immediately grabbed my attention was the new keyswitch. They exist in multiple flavors and are not universally interchangeable. I'd start there...multimeter in hand, schematic within eyeshot. Verify the switching function of each key position and each lead at the harness connector. There may be a wiring mismatch, despite the connector shell halves fitting.

Next up, the circuits that are powered-up as soon as the key is rotated to the "on" position: brake light, horn, neutral light, turn signals.. Could be something as simple as a single reversed pair of bullet connectors.This includes the rectifier, HL, speedo, TL...looking for one that might be reversed (+) for (-), or shorted...like the horn or tail light. There could be a short caused by an insulation rub-through...4 turn signals and the rear brake switch pigtail are obvious places to look.

Compared to a K0-K2 model, w/o signals and most of the handlebar switching controls, there's significantly more things that can go wrong. That said, even a `90s model electrical system is still quite basic...a.k.a. simple. The "nuclear option" is pulling the wire harness and verifying every lead, on the bench...unwrapping it, if you find a problem, or want to be extra-thorough. They rarely have defects but, rarely isn't the same as never. And, that'd allow you to solder the splices...which are simply twisted & taped. Still no luck...pull the remainder of the electrical system, then verify & check every lead & connection; that's a lot easier on the bench than it is in-situ, i.e. on the bike.

 

[theraymondguy]

I had my post half written before noting Racerx has already made note of the potential keyswitch/harness mismatch conundrum.

Sorry for the interruption, game on.

 

[allenp42]

Late to the party, but since I have a K1-76 switch in my hands and a partial K0 switch, I did a quick and dirty "paper exercise" to see what I would expect result would be if you had a K0 switch installed in your K4.

With the Key off, nothing should be getting hot, battery voltage should be ok.

As soon as you turn it on (pos 1 or 2), You will be taking the positive side of the battery to ground (earth) via the key switch. I would expect the fuse to blow immediately....assuming the PO did not substitute a much larger fuse.

As far is the rectifier getting hot, if you started the bike, then YES, the rectifier would get hot because the charge voltage is going directly to ground thru the rectifier.

Another tidbit. Remove the key switch, or the large harness grommet one the side of the frame, and see if you have a blue wire coming from the back of the switch to the plug. All of the K0 switches I've see have a blue for the "BAT - " connection whereas the same pin on a K1 - 76 is Red/white going to Terminal BAT1.

I've attached a K3 drawing with the K0 switch arrangement taped in place of the correct switch.

 

[Lex]

I found it. It was the stator/alternator shorting to ground. That explains why it was drawing voltage even with the key off. This was a brand new stator set. That goes to show that even new parts can fail. Thanks for all the help.

 

[69ST]

I found it. It was the stator/alternator shorting to ground. That explains why it was drawing voltage even with the key off. This was a brand new stator set. That goes to show that even new parts can fail. Thanks for all the help.

Only too true and it can happen with virtually any part, from any manufacturer. FWIW, the last thing I'd want to do is cause paranoia. Defective parts are still the exception, not the rule. The trick is coming up with a reasonable balancing act. IMHO, that's a mix of pre-install inspection, careful assembly, trial-and-error testing (normal assembly counts) and a process for sorting things out when something unexpectedly goes pear-shaped. It's really no different than what happens with brand-new vehicles, except that you have to be your own technician/diagnostician and the parts may take longer to get...or not. Takata airbags, anyone?

 

[allenp42]

Just a thought before you purchase a new stator lighting coil. Are you sure the rectifier is wired correctly? If it's reversed, current from the battery will flow through the one of the lighting coils even when the switch is off.

If the rectifier is in fact wired correctly, then I would expect that your rectifier is also fried (shorted).

The lighting coils have a very low DC resistance (<1 ohm) and it's easy to mistake a good coil to one having a short.

 

[69ST]

Just a thought before you purchase a new stator lighting coil. Are you sure the rectifier is wired correctly? If it's reversed, current from the battery will flow through the one of the lighting coils even when the switch is off.

If the rectifier is in fact wired correctly, then I would expect that your rectifier is also fried (shorted).

The lighting coils have a very low DC resistance (<1 ohm) and it's easy to mistake a good coil to one having a short.

That brings a horrifying thought to mind. The lighting/charging coil has two outputs. This is a dual-wound coil, with one end of each run to ground. IOW, a tester will show continuity to ground when everything is as it should be. I hope you're not using this type of test result to make the call. I'd want to check coil impedance with an ohmmeter...and...test the rest of the electrical system (other than the ignition side) by feeding 6vdc power to both the yellow (HL) and white (charging) leads to verify that everything works as it should, with the coil removed from the circuit(s) and thus positively isolated/identified as the problem. If you get the same malfunction, using an external power source, then the coil is not the problem...and you just saved yourself the time and bucks of needlessly throwing parts at it.