Fixing Molly, a 1981 Honda CX500c

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Here are pictures of all the things done to Molly to get her to work well.

When we brought the bike home, the first thing we did was change the handlebars. CX500 Customs have hangar handlebars like cruisers. The hand position is really uncomfortable and can cause tendinitis. Besides, I have a fractured forefinger (hairline probably), and during the ride home, whenever possible I had to shake the pins and needles from my hand. Not good positioning.

Me on Molly, a 1981 Honda CX500c, testing different handlebarsTesting different handlebars

The right blinker wasn’t working and the battery wasn’t holding its charge, so Jason tested the rectifier– that was good– and I removed the headlamp to look at the wiring. What a mess!

Messy wiresThese wires were hanging out the back of the headlight fixture, tangled in a ball wrapped in electrical tape.

Someone had spliced in extra wires to attach flasher relays. A bike only needs one flasher relay connected in series to the switch. But this bike had two flashers wired in after the switch. The right flasher was wired incorrectly, hence non-working. Plus, hot wires were exposed, which means the power was going directly to ground. That’s why the battery was discharging. Evidence of the discharge showed up on the starter relay near the battery, which was sprayed with dried battery acid.

I untangled the ball, removing connections that were done by a hack, and started pulling wires through the headlamp fixture, where they belong. There were lots of cut wires!

Pulling wiresUntangled!

After getting all the wires through, I called it a day. Next was retrieving the wiring diagram to rewire and get everything working properly.

All the wires pulled through the fixtureIt already looks better.

Since the harness is different from the original, I had to go by several wiring diagrams in order to understand which wire went where. Unfortunately, each diagram had a different key. One diagram used the letter “B” for Black. On another plan, it was Blue. Aw, geez. I had to make lots of notes.

Original Honda CX500 wiring diagramThis is the original Honda CX500 wiring diagram before the Custom came out. This diagram helped most. Some of the differences were drawn in. All the dots that are circled is where wires needed reconnecting. If you double click on the picture, you can see it bigger.

This next diagram is the addendum to to the Honda manual. Unlike the harness Molly has, the following diagram has only one black wire in the harness. Molly’s harness has two black wires running through. This explains why the previous electrical hacker cut so many wires trying to make it work.

Honda CX500 wiring addendumThis is the addendum to the wiring diagram with notes for the different models. I circled the power line connectors to figure out why Molly’s lights weren’t working properly. That didn’t help much. Though, it was from remembering this diagram that I realized that that circuit simply wasn’t getting power.

Did I mention I made lots of notes?

My sketch of the blinker circuitSince the existing diagrams didn’t match, I made my own diagram to figure out the problem.
The Haynes Honda CX500 wiring diagramThis is Haynes’ Honda CX500 wiring diagram. I used this to figure out which power line needed a splice. See where it says “4 way connector”? That’s where the additional brake lights are going to go after reducing blinker power.

To get the blinkers working, I used the gray and black wires in the harness, unlike the original CX500 manual, which says they run through the headlight fixture.

Flasher relays are polarized. You have to match the correct terminal to the power source. In this case, the black wire goes to the positive side of the relay (I think. I’m not sure because this relay has an “X” instead of a “+”). The gray wire returns to the lights via the switch. In my sketch, I drew two power sources: one through a fuse, the other from “power.” I’m not sure why I drew it that way. Probably because of all the diagrams I was trying to reference. I ended up going through a fuse, because of this diagram I found on a website.

Someone's flasher diagramIt looks like the person who drew this might be an engineer. I think I’ll trust this and go through a fuse.

There was a spare brown wire, probably for cops to attach a siren or something. I used this for the blinkers since this line only powered the lights in the tachometer and speedometer. If I ever put in something like handwarmers, I’ll reroute the blinkers to the main power line and install a heating element through that fuse (maybe). Besides, my new blinkers will use just a little power and will need a thermistor or some other resistor to keep them from shorting. But, hey, if you know better what to do, please comment!

Relocated flasher relayTurn signals only need one flasher relay. The switch controls which lights are connected to it. (That’s soldering flux in my left hand. It’s all Radio Shack had for flux.)

After testing the relay, I had to clean up some of the connections, and tighten others. Once all the connections were clean and insulated, I put the wires together for the headlight to go back on. The 7-volt regulator (not the same as the rectifier/regulator combo unit) sits outside the fixture. Wires were wrapped and pulled out to make space inside the fixture. In the end, all the original plastic connectors, and newly soldered connections were inside the fixture.

Organized wires in the headlight fixtureThe wires reconnected and reorganized! It’s not advised to use those blue connectors permanently, by the way. But making sure everything worked, it sure was handy having them. When I change the bulbs to LEDs, I’ll solder and heat shrink the connections.

She works! (Picture to come.)

2 Replies to “Fixing Molly, a 1981 Honda CX500c”

  1. I was really excited to come across this blog, as I just got myself the same bike but upon viewing, it seems none of your pics work anymore.

    I know this is a really old blog but I’m sad nonetheless. Hope it turned out well, though! Happy riding!!

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