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Discussion Starter · #1 · (Edited)
There I was, a few weeks ago, sitting at a red light on a divided, four lane road with a 55 mph speed limit. I was the only vehicle at the red light. I felt vulnerable to a distracted driver rear-ending me.

I decided to rectify the situation.

Perhaps you don't want to do this, but read on - this guide should work for almost any wiring modification you want to do for this era motorcycle. Sorry if this is wordy - it's a problem of mine.

I did this mod to a 1981 CM400E, but I've done other electrical work on a 1979 Honda NA50, which is a 6V, 50cc, two-stroke Honda scooter. It doesn't sound like they should have much in common, but Honda is conservative, even down to the wiring colors. I suspect any Honda motorcycle, scooter, or moped from this era is wired in a similar way.

For the flasher mod, I picked up the following:

I also have 40 x Motorcycle Bullet Connectors Covers 3.9mm Terminals Male/Female & Double on hand from the NA50 mod I did previously. This is $7, via prime. Pick them up if you are doing any wiring modifications or repairs, they last awhile.

Don't worry too much about brands for any of this, I'm just posting links as examples. I went with any product that had 4+ star ratings, and were cheap. I went with the LED taillight because I hoped it would be brighter (it is, but not that much more), and because I worried about a regular incandescent burning out faster due to being flashed.

The flasher is about the size of a quarter, with five wires coming out of it. One is a ground wire. Two others control the flash rate - connect them together to make it flash more quickly, leave them disconnected for a slower flash. The final two wires are meant to connect to the existing brake wire. The instructions say cut the brake wire, then connect the red wire to the wire coming from the brake switches, and connect the yellow wire to the wire leading back to the brake light.

But we don't need to cut anything at all. I traced the wires from the brake/turn signal clusters. They should end up at bullet connectors somewhere, probably under a rubber boot. On the CM400, I found the connector under the seat, hidden beneath the little tray that holds the owner's manual. The color scheme Honda seems to like to use is green for ground, brown for running lights, green with a stripe for the brake light, and orange/cyan for the turn signals. But check the wiring schematics to make sure.

If you disconnect any connector except the ground, the appropriate light should turn off, and all other lights should work normally. If you disconnect the ground, weird things happen. Honda likes to try to ground through the frame as a backup, but this isn't fool proof. I've noticed that a broken ground wire tends to create weird problems, for example, turning on the turn signals will make the tail light flash instead, while the turn signals won't light up.

The bullet connectors are the key to doing reversible wiring mods. They allow taping into the existing connectors on the motorcycle. I also had some extra wiring (which I didn't need) and a soldering iron and some solder. I suck at crimping connectors, so I like to solder them as well just to make sure.

The bullet connectors usually use a female connector for the "upstream" connector. If the connector works loose somehow, the male plug can contact the frame and short out. By using female connectors and an insulated sleeve around them, a disconnected connector is less likely to short. Honda engineers were good. Sometimes remarkably cheap (the NA50 uses the battery as a voltage regulator), but good. Use the same convention for any modifications you do - female where power is being supplied, male where power is being received.

I disconnected the green with yellow stripe connector, and tested everything - all but the brake light worked. I then added some bullet connectors to the flasher - remembering to slide the insulator on the wire first (don't forget). Make sure you have the appropriate gender for each bullet connector. I was prepared to make a short jumper for the ground, with a single connector to plug into the existing ground bullet connector, and a double connector to give me an extra port to tap into. That jumper works to double up any connector. But on the CM400, I hit pay dirt - the existing bullet connector was a double connector, with one side not being used.

That's it. Make sure to test all connectors that you've added to make sure they don't easily pull off the wire. When you attach connectors together, make sure they don't pull apart easily (I use a small needle-needle-nose pliers sometimes to fasten things together). Remember rain and wet roads, and stash anything that shouldn't get wet in a protected place. Doublecheck the results as well, and test everything - turn signals and brake lights should work.

Now this was just a flasher, but it could be anything. Want to add an additional running light? Just follow the brown (running lights) wire until you find a connector. Want to add one of those bar-end LED turn signals? Find where the cyan and orange wires have a connector. Remember that green is usually ground (check the schematics or with a multimeter). If you want to add a battery tender, break out the multimeter and find a connector that's live even when the kill switch and ignition switches are off. If you want to add a USB port or cigarette lighter, find a live wire that turns off when the ignition and kill switches are off.

And remember not to overload the alternator, or you will run down your battery. Converting some of the running lights to LED should help conserve energy. If you include turn signals, don't use resistors to make it work, but switch to a flasher that works with LED turn signals.

The advantage to doing things this way is that anything can be reversed - just remove your wiring and plug everything back together again. If some modification fails on the road, you can bypass it and revert back to the stock configuration. If you sell the motorcycle (which I'm told some (possibly deranged) people do), you can remove your mods.

I hope this helps someone, and it isn't redundant.
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