Aftermarket Ebike Wiring Harness For YT Decoy

Have you tried to contact YT USA? Someone said that they're a separate entity and still around in another thread.

Damn. Perhaps one of them will see it here and help you out? Maybe change the title to include YT?

I wonder if -as a last resort- you could use a wiring harness from another brand? It may be possible to find another brand's Shimano Ep801/STEPS parts and cross-reference them to your bike. I'd bet the bike brands use Shimano-supplied parts, rather than manufacturing them by themselves. 

EDIT: I do know a guy who rewires automobiles for law enforcement and movie studios. He's phenomenally busy, but may be able to advise you or even repair or reconstruct your existing harness: https://ejcommercialautoelectric.com/ 

Soap box context for the opinion shared within my post below: I ground up built a new wiring harness for my 99 turbo miata when I was still doing track stuff with it, and then re-harnessed it yet again when I put a honda k24 engine in it.  TLDR, I am VERY comfortable with DC electrical systems and wiring harnesses.  

It would not be a difficult task in theory to build your own ebike harness.  The tricky part of it is going to be using a donor harness to source the connectors and then splicing in new wiring to connect the dots (splices).  The problem with ebike harnesses is the sheer amount of abuse/vibration they will see.  I would recommend raychem solder grip (solder sleeve) heat shrink supported splice connectors.  These were invented for usage by nasa, so they are vibration/dust/fluid sealed and are the only effective way to solder splice connections without the conductors breaking at the solder joints.  

So... the first part of this process is doing QA/QC of the existing harness to figure out where the issue is.  IE, if it is in the connector or in the wiring harness itself.  I've seen a few harnesses that have chafing from the rough/inside of the carbon frames, so inspecting the insulation would be my first stop on this train.  I have also seen worn out female ends of the waterproofed connectors on power switches, leading to poor conductivity.  

Lastly, if you're going through all of this effort, it's really important to make sure you are using known good connectors.  It sucks to go through everything only to find out one of the connectors you're splicing in is a problem, and undoing that is a real pita.  You definitely want to qa/qc the harness at every step of the way, IE finish a connector/splice and then immediately check connectivity.  Electrical gremlins show up with poor/intermittent connectivity.  

One of the problems with electrical systems is that amperage (current) spikes when voltage drops.  The quickest way for voltage to drop, is poor connectivity.  This is why you fry/melt electrical connectors when they are sloppy/loose and worn out.  

Second soap box from someone who has bare frame built up two e-bikes:

It’s pretty easy to make, modify or repin harnesses and connectors. I bought eminent e bike frames at auction and made my own harness. the shimano properitiery e tube connectors are fine. I also modified another harness to accept an on off switch I made. 

Second to what’s said above…. Your entire harness probably hasn’t failed there is probably one connection with high resistance or a pinch point where a wire inside of the insulation has been broken. 

Check all connections and places where a wire could be pinched. Look for corrosion on the connector pins. Look for white stretch marks on the wire insulation. Look for sign of wear. You will find your harness issue. 

Did you try your battery in your friends ebike to verify its operation? 

A wiring tech tip. All shimano e tube wires have a red and black wire inside you can remove the insulation and wire them to whatever. They do not solder well as they are tinned in some sort of alloy that normal solder does not take to. 

when I first built my eminent e-bikes I had a couple harness issues after washing or a super gnarly chunky long ride. I would usually check all the connectors find a loose point fix it and everything would be fine. Or dry up water. 

Shimano also offers a ep801 and ep800 manual which covers basic wiring for all shimano equipped e-bikes. the only yt proprietary part of the harness is the connector to the battery and charge port. 

Good luck!!! I think with some electrical theory googling and some time you can fix that e-bike. 

I built an ebike from scratch with out a manufacturer to help, you can do this!!!! 

I just used those shimano etube wires or like bulk wire from the wire rack. I wasn’t able to purchase anything. If you really go digging you will find random companies selling this switch or that….

you will have to use your battery connection and your main ep8 unit connector

If you don’t find any obvious wear point or corrosion or connector loose pin.

Then here is my take from the peanut gallery on how you would diag and repair your harness. 

get the frame side battery connector free enough to see where the wires are coming out out of it. There should be four or five wires. Each wire will be its own color if there are two of the same color one wire will have a colored line down it callled a tracer. Then remove the on off switch loosely to display its connector.  Then remove the motor side cover and bottom shield to reveal the ports on the ep8 unit. The main connector that handles the battery voltage and on off switch is the larger of the three it’s obvious it’s a big round one. That connector spins counter clockwise about between 45 and 90 degrees after rotating it you can pull up on it and it will release from the ep8 unit. For the display unit and speed sensor they are there own thing with the etube wires you shouldnt need to mess with them other than checking for corrosion and connection. When removing any etube wires from its port I recommend using the shimano etube removal tool it works way better than just pulling on those tiny wires.

Once you have access to all three connectors on off , battery hook up and ep8 unit main connection you should be able to see the 4 or 5 wires coming out that will be that same 4 or 5 wires at the battery connector and you will see the on off switch wired in into two of those wires as well.

Try to draw a map of what’s happening connecting the connectors and the wires drawing lines connecting them. it can even look like a four year old did it. Ex  Like green on far left I’ll name that 1 it goes to top right in ep8 round main connector. I’ll also name that one for the battery connector. I would draw a rectangle for the battery connector and put lines for the pins like I read a book. For the ep8 main connector I would draw a circle and put lines in the circle to mimic the pins. Numbering them like in read a book also. 

Get a volt meter google how to put in ohms to check continuity. Then Check continuity from each connector using your map like green wire I’ll put the meter on 1 and 1. I would back probe each pin with a T pin to avoid damaging the connector. There are many YouTube channels on how to back probe a connector with a t pin. Then check continuity of every wire and were it goes with your map. Maybe draw an x at each connection you checked so you don’t get lost.  At some point you will find a wire that doesn’t make the meter beep or have continuity. That will be the one. Then Obtain connector depinning tools Amazon has many sets. Remove your failed wire re attach a new wire to your old connector pins or buy new pins if you can find them. some bike company’s use run of the mill electrical stuff readily available. some companies use stuff they have manufactured specific to them. You may not need the connector pinning tools. You may be able to cut the wire 4 or 5 inches up from the connector and use the nasa rated connectors mentioned above earlier. 

Well good luck that’s about all I have lol. 

I have a decoy too. I bought in September hopefully it lasts a while…… I’m sad yt is gone, mainly I just had a 150 dollar credit I wanted to use lol… 😂 lol

I have an uncaged 10 that is the same as a core three decoy. I had a problem with the bike, shutting off intermittently. I  get the motor to restart by pushing the on button. I did have one time where I could not restart the motor using this process. I  removed the battery and noticed there was one solid green light and one flashing light, I called YT when you could still get someone to answer the phone And they recommended charging the battery cleaning the connections and re-trying. My result was still the same one solid light and one flashing light after I tried to turn the system on. I contacted YT again and told them my issue and they suggested I file a warranty claim. After a few days, someone got back to me on my warranty claim. They stated the problem was likely a bad wiring harness. After digging around on the Internet and talking to some friends that have EP8 (mine is an 801) about spinning the motor backward to energize the control, allowing the bike to restart. When my bike had failed, I could never get the monitor to illuminate. I tried this process And to my surprise the monitor came on. Meanwhile, I’m waiting for a harness to come from YT under warranty. It sounds like I may or may not ever get the harness. Luckily for me, my bike has been working for the last few months. Not sure if this is a similar issue for you, but I got my bike to work.

the old spinning the cranks backwards trick has got me out of trouble too many times now.

I think the main issue is the small battery/capacitor in the ew-sw300 on/off button failing. It won't boot the system if that battery is flat or failing.

My button works maybe 50% of the time, or I just put a 5mm allen in the cranks and reverse kick start her lol

This is the real deal, a top mtb messageboard submission of all time!

I wish you were my neighbor. 

The harness and connectors on my transition relay seem to be the weakest part of the system 

They need to be more robust for a Mtb that gets used hard, probably the same with the YT stuff. Probably work great on a commuter bike tho