Rear tail light and stop lamp always on

[Petcha2]

Working on a 1977 XS650. Swapped out the master cylinder because okd one was pretty beat up, and I also wanted a mount for a right hand mirror. Installed and re-connected the two wires (Gr/Y and Br) to the same connectors behind the headlight mess as the previous one (which worked). Put the headlight back, bled the cylinder/front brake, re-connected the battery, and turned on the key. Tail light and stop lamp on instrument cluster came on - although I was not touching either brake. Brake light was fine, i.e. it only came on when you used the brakes, before I changed the master cylinder - which came from MikesXS. Any thoughts?

Sorry if this has already been addressed somewhere. I searched the forums but found nothing that directly related or answered my question. Even the one entitled “Rear tail light always on”. Maybe I should just put the old one back and forego the right mirror?

 

[Jan_P]

A friend with a Honda had problems of this kind
It was an adjustment of a switch position ..Since the master cylinder has been replaced I would check that the
Switch is at the right place and wires are OK ..to that switch

 

[member28833]

Guessing that your new master cylinder does have the brake switch that the lever bumps?
If that switch is not functioning properly your rear brake light stays on..
learned that recently

 

[Petcha2]

Yes, there is a switch that the lever bumps when you squeeze the front brake. The fact that the light immediately goes on suggests that this switch is defective? How might I check this?

 

[Petcha2]

Update: yep, the switch had shaken loose in shipping (I guess). Took it off, tightened it up, all good now. Thx to everyone who commented. Lovin’ the XS650 forum...