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Faulty second hand road legal electric scooter, engine continuously runs, 36v

Hi there, I am new to electric scooters/moped and recently bought a second hand one that was sold as seen for spares or repair. It was working order but batteries were only strong enough to turn the wheel when in the air, not with someone sitting on it. At this stage the throttle worked fine. All lights, brake light, indicators and dash worked.

I got it home, bought new batteries and fixed them properly. From hereon the problems started. The back wheel turned around backwards continuously so i reversed the polarity putting -36v into the system, the wheel turns the correct way but again continuously. Because of this, turning the throttle makes no difference. But wiring was getting hot! With or without the throttle connected the wheel turns continuously. The wheel turns correctly when i put in +36v and change over the wires at the speed controller for polarity so not necessarily a problem there.

So, I took bike to bits and it had obviously had a bodge job at re wiring in an earlier life. I replaced the speed controller for a brand new one and fixed it. Again the wheel turns after one click on the ignition, the second click nothing happens, the power goes dead.  The brand new speed controller, with just wires for power and motor and ignition will set the wheel turning on its first click with keys, dead on second click. When fully linked up, the electrics all seem to work but hitty missy, the dash can be on one minute, off the next. I have been testing by using just a one 12v battery rather than full power as it does the same job (not needing it to ride at this stage until fully functioning with throttle).

I am uploading pictures to see if anyone can identify it and if anyone knows of a  place that can supply the general wiring loom/harness. I figure a good wiring system is paramount to at least rule out other possible problems and not run hot.

The speed controller is available on this web site so hoping for compatible wiring harness/loom. This is the speed controller: 


Sorry for the long introduction but hopefully someone out there can help me!

Thanks Colin.

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To start off I do not know where to find a wiring harness for that scooter, and in all honesty I do not think that you will be able to find one since the brand of the scooter is not known. Even if the brand was known most scooter companies do not provide wiring harnesses for their scooters since they can usually be repaired instead of replaced. I understand that the wiring harness has been modified before you owned the scooter which could make repairing it difficult, if not impossible.

From reading your description of the problem, and please correct me if I am wrong, the rear wheel rotated in the correct direction with the original batteries in the scooter, although not with enough power to propel the scooter with a rider on it. And then after the batteries were replaced the rear wheel rotated in reverse. The only way I can imagine that happening is if the new battery pack was wired in the opposite polarity that the old battery pack was wired. Reversing polarity is the only way to reverse the rotation of a brushed DC motor. Brushed DC motors can handle polarity reversal, however speed controllers can not. Most speed controllers will immediately experience catastrophic failure if the battery pack is connected to them in reverse polarity. Symptoms of catastrophic speed controller failure can include run away scooter syndrome where the scooter will run at full throttle continuously regardless of the position of the the throttle.

If the battery pack is connected to the speed controller with the proper polarity and the motor rotates in reverse then the two wires between the speed controller and motor need to be reversed. But never reverse the two wires between the battery pack and speed controller.

If you could upload some photos of the battery pack with wires attached to the batteries, and the wires between the battery pack and controller that would help a lot to diagnose the problem. Without actually seeing what is going on I can only guess what the problem is.

Regarding the wiring harness I recommend basically starting from scratch and rewiring the scooter from the ground up. You could start with the basic task of getting the motor running and then move on to the lighting and horn. Having a multimeter

to test which wires go to which switches is a must in order to get the power, lights and horn working.

Looking forward to seeing some pictures "under the hood" of the batteries and wiring.


The original set up was putting -36v through the system but turning wheel correct way because the wires to the motor were also wrong. I can now put +36v through to the controller which now sets the motor turning the wheel in the correct direction (I changed the wires controller/motor). So, from a power point of view I am happy that correct polarity and power is getting to speed controller and motor.  I am wondering if polarity was wrong on purpose as since changing it all around I have lost some of the electrics. I think it is not wired correctly but may have to narrow it down to smaller chunks of information.

Some wiring works, some wiring does not. All lights work front and back. However, indicators do not flash, simply remain constantly on when initiated (this was working fine day i bought it). The brake light at rear is only other non working light, but the general red rear visibility light does work fine (again this was working fine day i bought it).

The horn does not work, was working day i got it. This may be easiest first step if anyone can shed light on it.

The throttle   does not work properly. Well, cannot test it as the wheel is spinning full power regardless of connected or not.

Speed Controller I have is brand new but i am beginning to suspect it may have been broken when shooting through -36v. 

On the dash board power light, indicators (work but constant), back light dash all work. However, speedometer and power level meter do not work.

Next to throttle there is a red button (separate from throttle) which says S-P. This seems to be wired to the two blue 'lock' in the controller. It also says on a sticker that this much not be deactivated to be road legal. It presses in and out and holds in position.

When the front brake is pressed it does not stop the motor. When the rear brake is pressed i feel it is only stopping the motor by brute force as opposed to cutting it out.

There are several wires 'under the hood' that i am unsure about. A few pictures attached. The purple wire goes to the dash, but unsure where to link it to in order to make working. Unclear about the yellow blue and white ones, but suspect they are to the brakes in some way. One, in the picture, a 3 wire small mini connector goes to where the pedals are, must be a speed sensor but cannot see where its 'home' is on the wiring system. I suspect some things missing or rewired incorrectly.

Thats about it for now, but will add pictures and hopefully we can build on this system. I have a friend helping me that has fixed motorbikes and cars all his life, but this electric is not his strong point and needless to say mine either! Even knowing how many wires come from each component would be helpful, these spare wires cannot be good! Thanks for any help in advance. The long visible unplugged 3 wire is the throttle cable for your information in the last picture, it is multicoloured as been messed about with previously.

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If the motor is running with the throttle unplugged from the controller then the controller is burned out.

Electric scooter and bike controllers use MOSFET transistors which lock the power into the on position when they burn out. Reversing polarity to the controller almost always burns out the controller, however it usually does not burn out the throttle though so chances are that the throttle still works.

If the indicators do not flash anymore then the blinker relay may have burned out when the electrical systems polarity was reversed. The blinker relay is a small black plastic box and it is fairly inexpensive and easy to replace. I do not know where it is located on that scooter though so you will have to look for it.
Turn Signal Flasher

For the brakes to turn off the motor when they are applied, the brake lever switches need to be connected to the correct wires on the controller. I recommend using a multimeter set to 20K Ohms to test the continuity of the wires while someone is pulling on the brake lever and letting it go every few seconds to determine which wires go to the brake lever switches. The multimeter will read I for infinite resistance when the switch contacts are open, and 0 for zero resistance when the switch contacts are closed.

The same method can be used to test which wires go the the lights. With a good light bulb inserted into the bulb base the two wires going to that bulb will have zero resistance, and when the bulb is removed the same two wire will have infinite resistance.

The horn can be removed from the scooter and tested with the 36 Volt leads from the battery pack to confirm if it still works.

The speedometer and power meter may have burned out when the battery packs polarity was reversed, or they may still be working but have been disconnected from the main power supply somewhere.

Most scooters have key switches to turn the power on and off, and switches on the throttle such as the S-P button, usually are not used for the main power switch. That red S-P button could be used for the main power switch though if you want though, there is no harm in that. I have am not sure what the S-P on the button stands for. I have a feeling that it originally was for controlling the pedal assist (PAS) function of the original controller. In some countries electric bike can only be used on the roads if they are pedal assist, which may explain the sticker that reads "must not be deactivated to be road legal". It could also possibly be a speed limiter button which are commonly wired with two blue wires.

Purple wires are sometimes used for the battery meter on many scooters. I have no way to be sure if that is the way your scooter is wired though.

The 3 wire small mini connector that goes where the pedals are is almost certainly for a pedal assist sensor which is attached to the pedal cranks. The controller that is currently installed does not support pedal assist so those wire should remain unconnected.

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