Ignition System Variations

What variations exist for the CT70 ignition system? I am working on a CT70H (It has the manual clutch).

I am not a Honda guy and am confused by the K0 and K1 references. I believe that refers to the ignition switch – one has a triangular base under the locking ring, and the other (like the one I am working on) has a square base. Is there any electrical switching differences along with the physical appearance (I read somewhere they are not interchangeable)? Also, are there any differences in the wiring harness? I am aware that there is an older version that allows the bike to run without a battery and an older with a jumper as part of the battery connector which completes the circuit from the stator winding to the splice going to the ignition coil and the kill switch (ignition switch in OFF). So the later version harness prevents running without the battery hooked up (the jumper is required, not really the battery). Is there any other variations and is that jumper relating to the K1?

K0 switch has the triangular base, K1 is square. Swapping them requires using the matching model wire harness, of some circuit revisions...if you're good with a schematic.

If you runs sans battery, you'll be running sans bulbs, too. The battery is the system voltage regulator; without it, bulbs last about as long as campaign promises...that's why Honda configured the wiring as they did.

I think replacement ko ignitions came with a square back. As far as I know if there is a blue wire going to the back of the ignition thats for ko, no blue wire is k1-76 if its a 3 position switch, no blue wire and 2 position switch is 77-79. KO/K1 refers to the model the bike is, KO's were made from approximately mid 69 to early 71. K1's are considered 72's, k2 is 73, etc. The ko model was the only one that covered more than one year. Am unsure of any wiring harness difference between ko and k1 other than the k1's have a neutral light wire, k2 and newer will be different as they were wired for blinkers in k2's and blinkers came installed in 74 (k3). I do know if you put a k1 and newer ignition in a ko it will blow the fuses.

hrc200x said:

I think replacement ko ignitions came with a square back. As far as I know if there is a blue wire going to the back of the ignition thats for ko, no blue wire is k1-76 if its a 3 position switch, no blue wire and 2 position switch is 77-79. KO/K1 refers to the model the bike is, KO's were made from approximately mid 69 to early 71. K1's are considered 72's, k2 is 73, etc. The ko model was the only one that covered more than one year. Am unsure of any wiring harness difference between ko and k1 other than the k1's have a neutral light wire, k2 and newer will be different as they were wired for blinkers in k2's and blinkers came installed in 74 (k3). I do know if you put a k1 and newer ignition in a ko it will blow the fuses.

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I have never been motivated enough to trace & compare K0 & K1 wiring schematics, or wire harnesses. The handful of keyswitch/harness mismatches I've run across resulted in blown fuses. It's much easier to just invest $35 in a new harness than to look further for the (likely) one difference.

hrc200x said:

I think replacement ko ignitions came with a square back. As far as I know if there is a blue wire going to the back of the ignition thats for ko, no blue wire is k1-76 if its a 3 position switch, no blue wire and 2 position switch is 77-79. KO/K1 refers to the model the bike is, KO's were made from approximately mid 69 to early 71. K1's are considered 72's, k2 is 73, etc. The ko model was the only one that covered more than one year. Am unsure of any wiring harness difference between ko and k1 other than the k1's have a neutral light wire, k2 and newer will be different as they were wired for blinkers in k2's and blinkers came installed in 74 (k3). I do know if you put a k1 and newer ignition in a ko it will blow the fuses.

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Thanks for the response. I'm gonna have to go back and look at the schematics I have. I had noticed the jumper on the black line but missed the blue wire difference. I am working on

hrc200x said:

I think replacement ko ignitions came with a square back. As far as I know if there is a blue wire going to the back of the ignition thats for ko, no blue wire is k1-76 if its a 3 position switch, no blue wire and 2 position switch is 77-79. KO/K1 refers to the model the bike is, KO's were made from approximately mid 69 to early 71. K1's are considered 72's, k2 is 73, etc. The ko model was the only one that covered more than one year. Am unsure of any wiring harness difference between ko and k1 other than the k1's have a neutral light wire, k2 and newer will be different as they were wired for blinkers in k2's and blinkers came installed in 74 (k3). I do know if you put a k1 and newer ignition in a ko it will blow the fuses.

Click to expand...

Thanks for the response. Interesting. I have to go back and check the schematics I have. I noticed the jumper in the black line, but missed difference in the blue. I am working on my neighbor's CT70H and he is a stickler for keeping it original. The restorer he purchased it from was more of a make it look good, if it runs its a plus, and parts are parts... So I have had some challenges. As far as I understand, the H was only 70-71. It has a square base ignition switch and has the blue wire which is battery to the switch. It has three positions, off (grounds black ignition primary), Run or "Day", and Run/On or "Night" which connects the blue to the taillight circuit (includes the instrument cluster backlight). No neutral light or blinkers. So it seems it has the correct ignition switch and harness.

One bit of testing I do, with custom wiring, is verifying continuity of every lead of the keyswitch, key in all positions.

It's possible to make just about anything work, all the switch does is close/open circuits. You've got ignition...grounded at the primary (kill) and not grounded (run), lighting circuit open/closed...one AC circuit (HL) and one DC circuit (charging/battery). Seriously, I've used early 3-position keyswitches with 6, 7, & 9 leads successfully with a 4-lead/12v/CDI harness setup and all lighting controls on the handlebars. That's why I said it depends upon how capable & comfortable you are with wiring & schematics. I've been doing this for a few...ummm...decades. It can still take me 1-2 days to completely setup a custom electrical system and some portions of the project are really slow & painstaking.

All of that having been said, with patience & persistence, plus a modicum of knowledge it's not really that complicated. And, bottom line, these electrical systems are about as simple as they get.

Unfortunately I need the patience and persistence. Looks like I am going to have to bench the harness. It seems to be giving me an intermittent open or short on the coil primary (I get a great blue spark, than zip). Also found all black wires have been tied together bypassing the jumper on the battery connector (basically like older style). Functional, but now suspect. i was able to locate a schematic specifically labelled for the CT70H. It came from Chilton which made me laugh. It was reviewed by the guy whose cube was one over from mine. He did all motorcycle wiring diagnostics and evidently minibikes too. That was more than twenty five years ago. The goal with this bike is twofold. Make it run, which it apparently has not done since purchased from a restorer, and the owner wants everything original like when he was a kid (so things like going to a CDI are out). But it is that very pretty candy emerald green, which makes me nervous about working without scratching...

OldRover said:

Looks like I am going to have to bench the harness. It seems to be giving me an intermittent open or short on the coil primary (I get a great blue spark, than zip).

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Are you speaking of the primary coil in the stator or the hi voltage ignition coil? I suspect you're referencing the HV ignition coil. If so, I'll share what I found a few days ago on an H that I'm working on. With the DVM checking the black wire on 4 pin wiring harness plug with the stator disconnected, I was getting zilch. Double checked that the 4 pin battery plug with black jumper was plugged in (and it was). Used some contact cleaner on the both ends of the 4 pin battery plug then I could read the coil resistance (2.5 ohms).

Oops, just noticed your 2 black wires are tied together. I would suggest you find the small black wire coming from ignition coil and check there first. It's rare to find a bad coil but a broken wire or bad connection is common.

Just in case you need it, here is the wiring diagram from an H Manual.

I'd run the primary coil output directly to the HT (secondary) coil input, bypassing the wire harness altogether. If that results in a consistently strong spark, the problem is wiring, not the coils.

I did jump the stator output directly to the coil primary and got a nice blue spark. I had replaced the remote high voltage ignition coil right after replacing the and getting it started. It had a poor spark and would misfire off idle. I also checked and confirmed all ignition components - stator coils (both ignition and lighting), condensor, and remote ignition coil. All good (confirmed original coil was out of spec). Also dropped in new points while at it. The ones in it were marginal so figured better to add some life. With the harness out it appears the restorer spliced two harnesses together. Explains issue with black wire (ignition primary and kill) as well as the dim taillight but OK instrument cluster (bad splice connection on tan wire). Now I have to ask the owner if he wants me to drop in new harness or repair the existing.
Thanks for all the responses.