Tail light short? No brake lights or horn after battery short with the frame. Anyone please help.

ZXS650

XS650 Member
Messages
6
Reaction score
1
Points
3
Location
san francisco
Hi folks,I am reviving my old XS650 and managed to short the battery with the frame by leaving a part ( the bike's turn signal relay - aluminum casing ) under the seat before taking it out down the block for a test. Rode for 30 seconds then the bike died, battery completely drained within seconds as well. no heat or smoke, no blown fuses .Took the battery out and hooked up a jumper . No sign of the bike electrical system turning on after turning the ignition key.

Jumper has an audible short warning for when the terminals touch and it gave the warning.Started looking around the harness and figured out that if I unplug the tail light - specifically the black cables- I am able to turn the system on, start the bike where it runs without the jumper or battery connected and I have the tail light on as well as the license plate light on. However I do not get any brake light action from either front or the back ( both bulbs intact - i checked and also tried different bulbs . and I also lost the horn ( I didn't check the horn up close but no visible damage like burned cables or terminals)I took a video of the situation.

Once I hook up power, I can turn the bike on once I disconnect the black cable on the tail light. Bike starts right up and I am also able to plug the tail light in and it lights up.

The battery ( brand new ) looks like it's recovering via a slow charger and once /if it charges I will put that in the bike and see what is happening with that set up.

As seen on the video the jumper when connected goes through a number of cycles before it turns off, the manual for it says that's normal as far as what the lights on the charger do, but I didn't experience the same thing when I used to hook up the jumper to a dead battery to work on bike recently. It feels like something is reseting
https://photos.app.goo.gl/irpgEYMi1qAyNSHD9

Also in photo below - the tail light has two bulbs - from the harness the sockets are connected via yellow cables. Somehow both bulbs light up even though only one of the black cables is connected . I inspected the tail light assembly and it looks like both sockets are completely isolated and separated from each other.

If anyone has any tips or thoughts I would really appreciate it.

Other than looking for another tail light and /or unwrapping the harness and trying to see if at some point the black / blue cable somehow got hot and perhaps burned a little bit and once under load it finally creates the short by touching something else, I am fresh out of ideas, I am also an absolute noob as far as things electric on the bike.

Thanks a lot in advance.
IMG_20250103_132745011.jpg
 
assume yourXS is either a SG,H,SH or SJ model (based on the two bulbs in the rear light). The black wire is ground, but it also runs to all the various component such as safety relay; ignitor unit, flasher canceling unit, rectifier and reserve light unit - so quiet a task to figure out where the failure lays, i would however expect that it's a short between the black wire and a hot wire, both will light up as they both get ground. Does your rear and front brake light work ? I would see if all works with the one black wire disconncted - also check that your system actually charge when bike is running.

If all seem normal you have isolated it to that one black wire, however you will have to follow it back through the harness as it may be connected to another black wire running through the system in find where the short is.
If you are worried about messing it up you could spend about $90 and get a new harness :)
 
What year model .?
Please test the horn via disconnect and hook the battery there

edit is it the light switch or ignition switch or the brake switch causing the red light on the jumper
 
Last edited:
What year model .?
Please test the horn via disconnect and hook the battery there

edit is it the light switch or ignition switch or the brake switch causing the red light on the jumper
Thank you. Its a 1981, The red light and beep on the jumper come on as soon as I turn the ignition key.
 
Thank you. Its a 1981, The red light and beep on the jumper come on as soon as I turn the ignition key.
The bike is at my friends shop across the bay, I thought of disconnecting the horn just as I got back. I will next time I go over. I had a thought of the horn getting bunch of current potentially as its mounted to the frame. but it looked normal at a glance.
 
assume yourXS is either a SG,H,SH or SJ model (based on the two bulbs in the rear light). The black wire is ground, but it also runs to all the various component such as safety relay; ignitor unit, flasher canceling unit, rectifier and reserve light unit - so quiet a task to figure out where the failure lays, i would however expect that it's a short between the black wire and a hot wire, both will light up as they both get ground. Does your rear and front brake light work ? I would see if all works with the one black wire disconncted - also check that your system actually charge when bike is running.

If all seem normal you have isolated it to that one black wire, however you will have to follow it back through the harness as it may be connected to another black wire running through the system in find where the short is.
If you are worried about messing it up you could spend about $90 and get a new harness :)
Thats a lot of helpful info, thanks a lot! Neither of the brake lights work and neither does the horn. I feel like I need to see how the bikes does with a charged battery instead of the jumper and I definitely wonder if I would be able to swap the harnesses. Looked like just routing and connecting, I am not sure if there is any potential need for soldering etc. I really appreciate your time and tips!

PS. The short occurred right next to the reserve light unit, somewhere between the positive batt terminal, frame , fender and the RL unit. I will check for any black wire going to it.
 
Last edited:
It could be the reserve light unit or light checker which could be eliminated - there’s a write up somewhere on this site how to do that. There are connectors within the harness the connect 2-3 black wires ( as well as other colors that runs through the harness) they all have shrink wrap around them and they may very well be soldered under the wrap - never checked )
Your horn and both brake light switches are connected via the brown wire which is hot, the horn sircuit is closed when you push the horn bottom - which then connect the pink from horn bottom to horn and ground via the horn bottom. Same goes for switch which close the circuit to either g/y (front) or y (rear)

It’s a royal pain in the neck to follow the wiring - if you don’t have a schematic download it from the tech site !
 
It could be the reserve light unit or light checker which could be eliminated - there’s a write up somewhere on this site how to do that. There are connectors within the harness the connect 2-3 black wires ( as well as other colors that runs through the harness) they all have shrink wrap around them and they may very well be soldered under the wrap - never checked )
Your horn and both brake light switches are connected via the brown wire which is hot, the horn sircuit is closed when you push the horn bottom - which then connect the pink from horn bottom to horn and ground via the horn bottom. Same goes for switch which close the circuit to either g/y (front) or y (rear)

It’s a royal pain in the neck to follow the wiring - if you don’t have a schematic download it from the tech site !
Thanks, yes I actually saw the write up for the LRU elimination earlier. Looks like Mikes XS harness for the bike is around 60.00 bucks, I will definitely look more into the installation etc. I do have the big book for the bike. Greetings from SF!
 
Thanks, yes I actually saw the write up for the LRU elimination earlier. Looks like Mikes XS harness for the bike is around 60.00 bucks, I will definitely look more into the installation etc. I do have the big book for the bike. Greetings from SF!
I’m working on rebuilding a ‘78 xs650e ( early model), the wires are a mess and I may end up buying a harness or use an European harness for that year which omit the light checker and the reserve light units, alternatively use a late ‘77 xs650d harness, as the ‘78 isn’t available. Did a ‘75 and another early ‘78 last year and the year before - both got new harness, it’s a lot easier than checking all the wires plus avoid a bunch of splicing :)
Good luck in your endeavor!
 
I’m working on rebuilding a ‘78 xs650e ( early model), the wires are a mess and I may end up buying a harness or use an European harness for that year which omit the light checker and the reserve light units, alternatively use a late ‘77 xs650d harness, as the ‘78 isn’t available. Did a ‘75 and another early ‘78 last year and the year before - both got new harness, it’s a lot easier than checking all the wires plus avoid a bunch of splicing :)
Good luck in your endeavor!
Thanks, same to you! I have only had this one XS, but for almost 20 years.
 
Back
Top