Light bar causes motherboard to reset on startup

I purchased a lightbar with my new E3v3SE printer (replaced an Ender 3 Pro) in January and just decided to install it. I followed the directions from Creality, including the doubling of the power leads.

Issue: once I power on the machine, it sounds like it’s starting up, and the mobo light turns on, then it dies. After about 5sec it tries again, and will continue until powered down. The display may be getting power, but it resets before the LCD turns on so I can’t be sure.

I’ve quadruple checked i have the right wire going in the right hole, ensured there’s no short between the mobo-connected leads, the light switch contacts are on their correct labeled I/O bits. There is no obvious damage to the wire, which isn’t under tension. Nothing else was edited on the mobo, all original glue intact. No foreign objects or wires crossing the mobo to create a short.

Pull out the light bar wires…everything is fine.

Is anyone familiar with what might cause this specific startup behavior? Or experienced this when installing the light bar?

Is it possible to light the bar when it is not connected to the motherboard socket? Just wondering if it is manufactured backwards ie positive is negative etc. Can you test it on a bench to a powersupply? Being diodes the electric can only flow one way. Had no issue fitting my lightbar but hey it could have been made wrong.

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I also wondered that, and was scared to switch them on the motherboard itself. I’ve not played with LEDs at all: is there an easy low-powered test you’d recommend?

24V 5W, got access to a benchtop powersupply?

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No, unfortunately. But sure seems like a good excuse to finally get one and test the other LED strips I’ve inherited from friends. Bar’s still under limited warranty, so I should probably also engage Creality Support. They’re currently replacing the original PEI bed, and the amazon replacement I purchased, that got surface damage from a cold print removal before I learned my lesson. Thanks for the help!

Not sure if a multimeter on resistance setting would work, not an electronics person, but it should pass current in one direction and not the other?

I’m not either, but it makes sense that I could test the switch connectors AND polarity now that I know diodes are one-way. It wouldn’t show me a working light, but it might at least show me incorrectly labeled wires. Unless a diode refuses to pass current under a certain voltage?

Might even show if an LED is mounted wrong too.

I have fitted this to my V3 SE with no issues, but did NOT install the same way.
My wire from the light to the motherboard runs externally and through the push out hole in the base at the rear right.
I may be wrong but the symptoms are indicating to me the LED wires are shorted together somewhere along the run.
If you have a multimeter you can check the wires for continuity and shorts then this issue can be isolated.
The Creality instructions on the web web show dissasembly of the gantry and to me this could easily create a pinch point for the LED wires which could cause a short if the wires are trapped.
Once working the LED lightbar in excellent.

Good Luck