I've got an issue right now where my taillight and brake light blink when the flashers are on. I didn't have this problem last riding season. I did however have an issue blowing out taillight filaments I never figured out. I blew another taillight filament on my first ride (5 miles) after I got the bike all back together from a bunch of winter maintenance.



I've exhausted all my ideas to correct this as well as DEETs. I've been communicating with him about this for the last couple weekends.

I replaced the handlebars and their hardware over the winter, the front flashers are grounded to the bars. I sanded the upper clamps where they contact the bars to make sure there was a good ground there.

I sanded the ground connection to the flasher relay and the ground connection at the coil and the contact piece coming from the wire harness that attaches to the coil.

Front and rear flashers are NOS, I'd bought/installed last year, and they operated correctly last year.

All bulbs are the correct 6 volt.

The pigtail from the taillight assembly was replaced winter a year ago with one I'd bought from DEET.

The bulb socket in the taillight assembly is clean, still looks like new actually.

I replaced the battery, and it's fully charged.

I replaced the flasher relay with a NOS one.

I checked all the wire connections from the taillight, brake light, both rear flashers and the flasher relay.

I'd installed a NOS voltage regulator, I've got the same problem with the voltage regulator hooked up or not.

All wire connections inside the headlight bucket look fine.

All the electricals work; tach backlight and flasher indicator, speedo backlight, high beam indicator light, headlight high and low beam, horn, tail light, brake light with both front and rear brake switch and all four flashers. Nothing but the taillight and brake light blink with the flashers.

 

Any other ideas gang?

Problems like that often come down to a bad earth probably at the tail light & its trying to earth through the other bulb filament. Look at the tail bulb with the lens off & see if the other filament glows every blinker flash. In hindsight i guess your tail is DC powered on all the time where ours are AC mag powered wit the headlight. But possibly still relevant what i said--earth problem.

50 year old wire. I had a '76 Kawasaki 900 that was original and unrestored. It was blowing a fuse intermittently. Spent lots of time troubleshooting looking for a short. Discovered a short in the bundle of wires from the right handlebar switch. When the cable ties were cut and the sheath removed and the wires separated the short went away. No visible wires were sticking out and the insulation had no nicks or cracks. But when the bundle was cable tied together and routed properly the short appeared. A new repop handlebar switch assembly with wires and connectors fixed the problem. I suspect that the insulation had deteriorated. Also I believe that modern wire and insulation is better quality. I've replaced 2 of my main harnesses with new ones from DEET. My goal is to do this for all of mine plus have him rewire the handlebar and key switch assemblies.

A bad battery may cause that too. When the flasher draws power to the signals it can show low voltage on the taillight/brake light making it dim and return in conjunction with the flasher. Head light won’t blink because powered from engine. Blinkers and taillight from battery.

Edit…oops I see you replaced the battery and is fully charged. The flasher works well and is nice and crisp in your video. Forget my suggestion above. I was just thinking about what I‘ve seen but I’m at a loss for yours. Seems like a short or wired together wrong. I always caution people to clean the insulation on those old dirty, oily faded harnesses so you can clearly see the color of the wires. You ALWAYS match color to color when connecting. Use plenty of shop lights or natural sun light. Double check color to color at EVERY connection on the bike. This doesn’t vary. Good luck.

Another odd thing i've been caught out by is the two filaments in the tail bulb [likely cheapy made bulbs] had leant over & touched together. That was a head scratcher at the time.

Brzn my CT1C does the same thing and I had a new battery too but when it’s running it doesn’t do that it works as it should 

I would say a better description from what I see is the tail/brake is "DIMMING" when the turn signal comes on.

Likely battery and/or wiring and/or connections and/or switch contacts cannot handle the amount of power drawn by having the tail/brake and turn signal on at the same time.

Could just be a weak battery? If you start the bike and rev it up while doing the test, this problem often stops.... doesn't sound like you'll be that lucky since you say new charged battery.

One thing you could try is probing connections with voltmeter... I'd start at battery. Negative meter lead stays connected to good ground... then probe positive battery post with positive lead on voltmeter. See what voltage does at battery with tail/brake on and flasher flashing. If it drops a couple volts, then battery can't deliver the amps needed.

If there's just a slight voltage drop at battery when signal comes on, then probe the fuse with positive meter lead... (negative meter lead stays connected to ground)... next probe the red into ignition switch... then brown out of ignition switch... Check and see what voltage does at each point with tail/brake on and signal flashing.

If you didn't have a significant voltage drop at battery, then you'll probably find a drop (or multiple additive voltage drops) as you move down the current path.

For example, say you have 6.2 volts at battery when signals come on... and about the same at both sides of fuse, at red into switch, etc... but then when you get to brown coming out of key switch the voltage drops to 4.5 volts when signal bulbs light up. That means the wires, wire connection, or contacts in switch are not able to flow enough current.

In other words in this example all is good up until the red into the switch... but then we see a significant drop so the problem is somewhere after the last good test point and the test point where we see the big drop.

Sometimes you'll find multiple small drops as you move down circuit from source (battery) to load (bulb) that add up to a couple volts as you get closer to bulbs. Easy to see. But a little harder to fix because as was mentioned the wire might be going bad and needs replacing or something like that. I haven't seen that too often though.

Keep in mind batteries aren't big so make sure to check voltage at battery as you go along to make sure drop is not just battery going dead.

There are other methods you can use with voltmeter to find bad connections but this one works pretty good for me most of the time.

Hope that makes sense.
...

Another method is to connect voltmeter across a connection... for example one probe of voltmeter to red into ignition switch and other probe to brown out. You should see 0 volts. But you might see a couple of volts when the load is applied (tail/brake and flasher all on). That would be a problem... there's a voltage drop between those two points under load.

This method works for grounds too... hook one meter lead to battery ground and then probe ground points with load applied... voltmeter should stay at 0 but if you get a decent voltage reading, that ground is bad.

I had two thoughts:

First is 1971DT250's comment regarding old wire is certainly applicable to our machines at this point in time. One would be amazed (or, perhaps not) at the corrosion inside an otherwise "good" wire. His example of the KZ900 is very illustrative of some issues I have experienced as well.

Second thought is that MARKT's comments are spot on with regard to his troubleshooting advise. That was an excellent explanation of just how to find a potential voltage drop and pin down a problem. Print that one out and save it somewhere guys! 

KUDOS to you Mark!

Have you tried a solid state flasher to see what happens?
Have you checked the Wattage of all the bulbs?
 

MarkT GREAT explanation.     

Ps MarkT how do you print this out I want to save this