No Tail Light, but Brake Light Works

The tail light on my ‘82 XJ750 stopped working a few days ago. I still have a brake light when the brakes are applied, but no standing tail light. I checked with my meter and have voltage to the bulb terminals for the tail light. That voltage spikes when the brakes are applied as well. I’m a noob to electrical work, but I’ve done some reading and it seems I may have an issue with the tail lights’ ground. Seeing that I have voltage for the standing tail light, what should my next step be to resolve the issue? As always, I appreciate all the great advice from everyone.

 

Are the taillight filiments burned out maybe?
When you are measuring voltage, are you using the socket ground?

 

I’m not sure, I can grab some new tail lights today to rule that out first. When measuring voltage, I just held one end of the meter to one terminal of the tail light and the other to the piece of metal above the tail light where the ground wire is currently attached to.

 

That's correct, with one lead on the ground you should see 12 volts on one pin in the socket with the key on, and 12 on the other pin when the brake lever is pulled/foot pedal pressed down. If there is no power the pin that lights the running light, then you'll need to work backwards from the light. Start with the bullet connectors that hook the taillight to the main harness.

New bulb is pretty cheap if you're not electrical savvy.

 

both filiments share the same ground
could ne the filiment is done for the tail light
i find the contact on bottom of bulb gets dented in and fails to make a good connection.


after checking the L/W blue/white wire at rear of bike check its connection at cluster same color wire

 

is the CMS (computer monituring system) lighting the tail warning? this would mean bulb is bad

 

The engine has to be running for the CMS to do the check.
Well, it has to have run anyway. An unstarted bike won't cause the CMS to check anything, but a bike that has started and then shut off will, as long as the ignition is still on.

 

Bad bulb check? Easiest way is to look at the filaments to make sure one is not broken. If eyes are not too god you can use a multi meter to check both filaments:

 

sometimes the filaments touch until power is added.
easy bulb check is to swap in a known good bulb.