[other_jim]

Howdy there fellas. I have a 1979 CM185 that I accidentally nuked the other day. The extent of my electrical knowledge has been dealing with a trio of 1964 C200s that were dead simple and $30 of gack let me swap them over to 12v. I tried the same thing on the CM here and she died immediately when hitting the start button.

12v head & tail, signal bulbs
12v universal rectifier intended for a C90 (plugged right in and crossed my fingers)
LED flasher relay
12v battery

On my older bikes, this is all I had to do; no condenser or ignition coil changes necessary. Here, though, I turned the key and all lights came on, but the start button killed everything - fuse is intact - and now key on/off does nothing, no spark, etc. my question is, I guess, what did I blow up? I'm a dunce with the voltmeter so I was hoping someone that knows the wiring on these things might direct me to what component I've gone and ruined, if not all of them. I wasn't expecting everything to die all at once like this.

 

[Scramblr]

Typical 1970's model Hondas had no fuse between the battery, starter solenoid, and starter. A 6v starter could be run with 12v but would likely spin very fast and possibly melt the windings inside on extended use.
I would suggest during electrical testing to disconnect the electric starter feed wire at the solenoid and then perform voltage tests between the battery and various circuits, like the coil, headlight, taillight, horn.
The one common leg of the entire electrical system is the frame acting as ground, attached back to the battery negative with one cable. Check that connection at both ends.
One shop manual for your CM185 can be found at Manualslib. Page 7 has the wiring diagram.
Let us know what you find so we can help.

 

[mike in idaho]

I would bypass the key switch first, the extra current draw from that 6v starter relay may have caused a problem with the contacts inside. The starter relay(solenoid) should be swapped out for a proper 12 volt part. If you want to get decent life out of the points & coil, the coil should swapped for a 12 volt version(at least 4 ohms of primary resistance). Or, keep the coil and add a ballast resistor to the circuit to keep the current draw at a reasonable level. A 6 volt starter motor will work just fine on 12 volts, as long as you refrain from grinding on it too long.

 

[other_jim]

I've gone and watched a few children's instructional videos on how electricity works since I've been working with 60s bikes like a caveman and stripping the battery and signals off them, running the bare minimum off the magneto.

I checked continuity on everything and most of it checks out. Starter motor has continuity to the switch, all the switch continuity checks out when in the ON position.

Issues with the ignition coil: no continuity from plug to battery positive. Otherwise all the wires going in/out of the coil have continuity to the battery positive.

I might order a new 12v coil and maybe a condenser as well to be safe, I'm not sure if this one is toast and I haven't been able to figure out how to test it.

The starter relay(solenoid) should be swapped out for a proper 12 volt part. If you want to get decent life out of the points & coil, the coil should swapped for a 12 volt version(at least 4 ohms of primary resistance). Or, keep the coil and add a ballast resistor to the circuit to keep the current draw at a reasonable level. A 6 volt starter motor will work just fine on 12 volts, as long as you refrain from grinding on it too long.

I was planning to just never use the starter and avoid the hassle, should to solenoid be replaced if only the kick start is used?

I imagine CM200 parts will slot-in fine but I'm not sure, the capacitor comes out of the coil under the seat on this thing, which is a significant difference from its location on the 200.

I did notice in the manual that she'll only make 8 or 9 volts at 5500rpm, so the 12v battery is probably not going to have a good time of it. It's probably worth never dealing with lead acid and 6v bulbs again, though, even if it means bringing a trickle charger all over the place.

 

[other_jim]

I've gone and replaced the solenoid, rectifier, ignition coil, all bulbs, plugs, battery, and none of the electrical works or lights come on when the key is turned. I am very confused. Is this a bad ground or something? I just don't know how that would have resulted from hitting the starter with a 12v plugged in, I assumed some component must have gone bad but I've replaced almost everything

 

[mike in idaho]

Power to the switch? Power out of the switch, with the key on?