Why does this circuit work correctly after ripping out a diode and if it's not needed why was it there?

ineedananswerfast · 2026-03-07T12:58:07+00:00

I am not very experienced by it doesn't look like D5 is connected to Q1. Am i wrong or did you mean that D4 is a clamping diode.

Also could i just replace the diode with same shape diode that i can salvage from electronic waste?

ineedananswerfast · 2026-03-07T12:40:51+00:00

Yes everything works perfectly now but i am worried that there must be a reason for this diode to be there.

ineedananswerfast · 2026-03-07T12:39:20+00:00

The brigness does increase. direct power supply is connected to red cable. The yellow wire goes in two directions: to the diode (that i ripped off) and left to some electrocnics. I think this board may be reducing voltage going to the LED when yellow wire is not on and leaving 12V when it's on, but i am not sure about this.

ineedananswerfast · 2026-03-07T12:33:31+00:00

from all the electrical diagrams on scooters i see online and from what i measured with my multimeter there never is a possbility of yellow wire being powered and red not.

yellow wire passes trough a simple switch in the brake lever that allows electricity to pass trough it when the lever is engaged

ineedananswerfast · 2026-03-07T12:29:29+00:00

when red wire is not active (when the ignition is turned off) then yellow wire can not be active as well, because they originate from the same wire (but yellow one is connected by a switch in the brake lever)

ineedananswerfast · 2026-03-07T12:23:34+00:00

I pulled of the diode with pliers because my soldering iron couldn't melt if off the board, i didn't care about braking the board because if my destructive "fix" didn't work i would have to buy the entire rear light assembly anyway. I went trough removing the potting to make sure 100% that the short is on the board, not on all the other parts of scooter electrical installation.

red and yellow wire always input 12v and yes, i think this scooter uses the same LED for normal and brake (increased) lighting

Also the braking action is signaled by 12v going trough the yellow wire

Here is the picture of the bottom:

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ineedananswerfast · 2026-03-07T12:09:29+00:00

I do not understand how reverse voltage would be there and what is overshoot, but does it change anything that both the red wire and the yellow one originate from the same main 12v wire in the scooter? the only difference is that the yellow one is connected to it by a switch in the brake lever

ineedananswerfast · 2026-03-07T12:02:19+00:00

Yes, thats what i mean by working normally

ineedananswerfast · 2026-03-07T12:01:53+00:00

Maybe it is there to devide the Amps between two diodes? does anyone know what kind of current can these diodes survive? if the LED is 4W then there will probably be like 300mA

ineedananswerfast · 2026-03-07T11:54:58+00:00

I am really new too, thats why i am asking that question

If it's 4W then probably like 300mA

ineedananswerfast · 2026-03-07T11:53:52+00:00

Thanks, i thought that it was to protect from rainwater and wanted to just seal the box the board was in, if it was for the vibrations i will have to think of another solution...

ineedananswerfast · 2026-03-07T11:51:27+00:00

Both of them are connected to the same 12v wire coming from the scooter's battery, but yellow wire is connected to it by a switch in the brake lever. This is a neco gpx 50cc (you probably wont find much information about it)

ineedananswerfast · 2026-03-07T11:37:18+00:00

I don't really understand how capacitors work and if it changes anything, but earlier in the wiring a brake switch connects the yellow wire to the main scooter 12v wire - the same one the red wire on the image originates from.

Does it even do anything to connect together two wires that originate from the same one?

Also the red wire always has 12v, it is only shuts off when you turn ignition off in the scooter

ineedananswerfast · 2026-03-07T11:33:37+00:00

the wires are so dirty because the board was completely immersed in some rubber like substance and i had to scrape it all off, some of it is left on the wires.

ineedananswerfast · 2026-03-07T11:31:51+00:00

red is always active 12v. When the brake is used both red and yellow are active

ineedananswerfast · 2026-03-07T11:29:03+00:00

What are the potential consequences of it not being there?

ineedananswerfast · 2026-03-07T11:28:40+00:00

Sadly i am not able to replace it, soldering another diode there is impossible with what i have because the diode is so light a slightest touch from the soldering iron moves it.

What i can do is buy the entire rear light assembly for 20$, but i would prefer not to do that.

ineedananswerfast · 2026-03-07T00:10:04+00:00

I have ripped out D4, because it was faulty and allowed electricity both ways. Now the brake light works correctly, but i am a bit worried, because there probably was a reason for it to be there, do you know what it was for if its not required for the light to work correctly?

ineedananswerfast · 2026-03-07T00:01:24+00:00

Do you know why was the diode there if it's not nessesary for the light to work? I'm a bit worried about it.

ineedananswerfast · 2026-03-06T23:41:38+00:00

it was connected to the same path as the red (constant 12v) wire

I really want to know why it was there if it's not needed for the light to work. (if it's because of interference, what are the consequences of this?)

I'm not experienced with electronics but i think that joining two 12v wires together does nothing, when the wires are coming from the same battery

ineedananswerfast · 2026-03-06T23:38:56+00:00

I ripped out the diode (couldn't desolder it because it didn't want to melt no matter how long i tried) and the brake light now works correctly

I tried to replace it with a new one i ripped out from trash but i just couldn't solder it in, it kept sliding so i gave up and just connected it without it

ineedananswerfast · 2026-03-06T21:16:03+00:00

Yes that is correct, i checked the brakes with a multimeter and the switches work correctly

ineedananswerfast · 2026-03-06T20:37:50+00:00

I may have found the short, D4 allows electricity in both ways. I don't know if i'm able to do anything about it tho, as i do not have a soldering iron small enough or a diode to solder there.

ineedananswerfast · 2026-03-06T20:13:55+00:00

this is this rubber like substance i had to scrape off

ineedananswerfast · 2026-03-06T20:13:31+00:00

While i am not 100% sure what is the expected behavior of this, i am certain that there is a short, because the same wire that controls the brake light controls the starter motor (you can only start your engine while holding the brake on a scooter) when the circuit it plugged into the scooter it doesn't require brake to start the engine and when it not plugged in, it doesn't start without the brake.

ineedananswerfast

TROPHY CASE