CT70 Taillight/Brake Light Issue

M

motoman287

Member
So I reassembled my '81 CT70 that was in pieces for several years. New battery, with key on I get my neutral light and brake light, meaning pressing the pedal or squeezing the lever does nothing, the light is always on bright as if the brakes are being applied. It doesn't dim when brakes are applied like I've read in a few other threads. When running, I get my headlight and high beam indicator, so everything seems normal aside from the brake light issue. I will recheck my ground, but is there something else I'm missing? The brake light switch for the rear pedal is pretty straightforward, no wires are crossed there, but is it possible I have something plugged in wrong inside the headlight bucket?

Thanks!
 
kirrbby

kirrbby

Well-Known Member
Bad switch maybe? Try unplugging the switches, on at a time to figure out which one is causing the always on. Then test the switch to see if it's bad. I think it should have continuity between the 2 wires, ONLY when the brake is applied.
 
hrc200x

hrc200x

Active Member
Are the two wires back at the tail light bracket crossed, maybe the tail light wire on the bike side of the wiring is sending power to the brake light wire on the tail light side of things
 
hrc200x

hrc200x

Active Member
You also may have a power wire plugged into the female green wire with yellow stripe in the headlight bucket, that appears to be the power wire to the brake light switches, then back to the brake light. I have a '80 wiring diagram in pdf format on the computer. If you need it text me and I could take a picture of it off the screen and send it.
 
M

motoman287

Member
Thanks guys for the suggestions. In order to bring closure to this thread, I will, embarrassingly, admit what the issue was...I swear when I put everything together, the bulb looked good. I didn't test it, just gave it an eye check. Apparently, at the ripe age of 30, my eyes are failing me. I took the lens off to look again at the bulb, and realized that although both filaments looked good, one was bad off to one side. I found another bulb in my spare parts, only to find that the other filament of that bulb was shot, lol. So, new bulb it is. I was able to check with the other bulb that both of my brake switches work properly though. I'm an idiot...
 
kirrbby

kirrbby

Well-Known Member
A mere oversight. Or undersight maybe... No matter it's a good fix, and done.

You might say...Guess I'm NOT a idiot. It was wired right, just had a bad bulb.
 
6

69ST

Well-Known Member
Don't feel bad, those filaments can appear to be intact, even under magnification...at least for a while. Eventually, of course, vibration will widen the gap of one that is broken. Only surefire method is testing both filaments, bulb removed from the bike. No idiots, or cause for embarrassment here, electrical diagnoses are costly (at repair facilities) for a simple reason...they take time to complete.
 
red69

red69

Well-Known Member
I just had a similar problem on my S90. I was thinking the new brake light switch was defective, but in all probability I checked it before installation. Anyway, neither filament lit up, so I checked the bulb. Both were good. My problem was the good coverage with paint when I did the rear light housing. I checked with a meter with the bulb removed and it had no continuity to ground. I wound up scraping (ugh!) off paint at the screw holes and dabbing dielectric grease on the areas. Stop light and tail light now work.
 
6

69ST

Well-Known Member
All you really need to do is chase the threads, to which the ground strap is attached, and you'll get a solid ground. If using the TL bracket-to-fender bolt, then chase one of the fender mounting bosses. An M6x1.0 tap should be part of the Honda owners toolkit.
 
red69

red69

Well-Known Member
Bob, if you are referring to my S90, chasing threads will not do anything. The tail light has a chrome back plate which has the screw threads. The screws pass through holes (larger then the threaded screw) in the bracket and the paint insulates them from being grounded. The mounting bolt from the bracket to the fender was grounded just fine.
 
basketcasek1

basketcasek1

New Member
kirrbby said:
Bad switch maybe? Try unplugging the switches, on at a time to figure out which one is causing the always on. Then test the switch to see if it's bad. I think it should have continuity between the 2 wires, ONLY when the brake is applied.
Click to expand...
My K1 also has demons in the tailight. Always on brake light. Have unplugged front brake line switch, still stays on. What other switchs can I try?
 
kirrbby

kirrbby

Well-Known Member
The rear brake light switch is mounted on the frame down by the brake pedal. It has a small spring that connects it to the brake pedal. See if the spring is adjusted too tight, or the switch is stuck. The spring pulls a little plunger rod out of the switch...try working that plunger in and out a few times.
 
basketcasek1

basketcasek1

New Member
kirrbby said:
The rear brake light switch is mounted on the frame down by the brake pedal. It has a small spring that connects it to the brake pedal. See if the spring is adjusted too tight, or the switch is stuck. The spring pulls a little plunger rod out of the switch...try working that plunger in and out a few times.
Click to expand...
You have just solved my issue! I had adjusted it yesterday when I was working on rear brake pedal travel. Figured it had to be something big. Thanks for your help, you're very good!
 
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