Thread: Tailight issue

Ok, wasn't getting tailight to illuminate, checked wiring and ground and re-wired along with proper ground. Now, when applying the foot brake, the tailight goes out. I researched previous posts and couldn't find anything. I know this was discussed, what's the answer. Ground on tailight is fine, connections on tailight fine. Help!

This might be a dumb question but, are you sure the bulbs good? There are two filaments inside the bulb. Ones for the tail light and the brighter one is for the brake light. I don't think they both illuminate at the same time. Check or change the bulb first to rule that out.

Brand new bulbs, both filaments good (intact). I just can't remeber what the answer to this one is, but it has been covered not too long ago. Grounds are metal to metal (no paint interference), all connections tight.

Is it when you use the just the rear/front brake levers or both? Perhaps the brake wires are grounded out. You checked all the wiring for breaks and/or chaffing?

It's both, and this is a ground up total restoration. New everything including OEM wire harrness. Wires are not kinked or pinched and everything seems good. This is what makes these projects fun, huh????

Maybe the wiring harness is bad. Can't rule that out. Where did you get it?

I found a guy that has OEM stuff from a Honda dealership and the wire harness was still in plastic in good shape. I may try another harness I have to check it out, but I hate to pull the tank and everything again. I wonder if I have a bad stop switch?

What color wires coming off the taillight? I also bought a new taillight and the colors were very mismatched. Taillight had red/black/black w/stripe. Let me know if yours is the same and I'll describe the wire-to-wire connections I made.

No, mine are standard . Green and yellow, brown, and a separate green (ground wire). All connections solid and tight.

It's a bad ground. As with any electrical issue on these bikes, the system is simple as are any problems. That doesn't make things any less frustrating while you're trying to locate the source location; trust me, I speak from firsthand experience. It's the really simple stuff, things that "couldn't possibly be wrong", that will give a real gearhead brain cramps. You already know that you're getting power to the tail light, the only other possibility is a ground problem.

Paint is a great insulator, as is grease; so are those rubber isolators on the tail light bracket. Rust/oxidation run a distant third. A quality repaint should come with a guarantee of at least one post-assembly ground problem and these can takes months of seemingly trouble-free operation before manifesting as tail light/brake light malfunction. Most common places for ground faults: ignition keyswitch, tail light body-to-frame ground, battery-to-frame ground, ignition secondary coil (which is irreleveant, in this instance). A multimeter and a pair of long test leads can make quick work of this. Everything in the lighting circuit is grounded to the frame...and back to the battery. Consider every ground lead part of a single ground bus. First thing I'd try is jumping the tailight ground directly to the battery, if that cures the problem, you're done. If not, repeat the process with the ignition switch body. You don't even need to remove the keyswitch, just run the test lead from the trim ring to the negative side of the battery. It's almost certain to be one of these, or something not connected properly. A wire harness defect, in an OEM harness, comes with lottery-winning odds.

Having said all of that, if you're still stuck after this bit of "expert advice" (worth at least what you've paid for it) then by all means let us know...and I'll happily don the blindfold once again for yet another dart throw at the electrical diagnosis board