I have a problem with my Di2 system. It doesn't work, no shifting, no light in junction box.

I've tried two different rear harness, and measured the battery voltage to 8.3v.

Any ideas what's wrong? I did search, but did not find. Maybe other sites with good information on Di2 troubleshooting.

Thx

step one is to check connectors for any corrosion on the plugs/pins. also check for any wire breaks. any place it's been ziptied is a possible break, if the ziptie was tightened excessively.
after that, youll need to bring it to a shop with a diagnostics box.

Have you tried a different front wiring harness?

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No, I haven't since I only have one set, but I figure that the failure would be there, since the battery should be ok and two different rear harness aren't working.

If one of either shifters or derailluers is not ok, would the other parts then work. Like if the fd is malfunction, would the rear then work?

For your symptoms, that nothing works, says that its one of the common parts or wiring. That eliminates the FD wire, RD wire and shifter wires. I had this once on one of my builds. It was the front connector that zip ties to the rear brake cable below the front JB. For some reason, that connector requires a lot more force to push together than the others and you can have it pushed together, without making a connection. Make sure there is little or no gap between the male and female on that connector. If there is a gap, remove the zip tie and push them together harder! Takes a lot of force.

Thanks.

I think you are right, its the front junction box that fails. I can measure the battery voltage at the wire coming from the rear JB going into the front JB, but I cannot measure anything on the other side, at the shifter connection. Shouldn't I be able to do that?

You should separate that connector, and then plug it back together with sufficient force to close the gap between the male and female of the plug. The light should then come on in the control box, indicating the system is ok.

Not necessarily, as far as I remember the front JB changes everything pretty dramatically. I remember our engineer saying everything forward of the front JB was a very simple system, but once it comes out of that it was quite a bit more complicated, so obviously there are some serious changes as it passes through the JB.

You are correct in thinking that a flaw in one piece won't necessarily stop the whole system from working. You can run Di2 when it's only partially hooked up, you don't need everything to be plugged in for it to work, which is why I'd be reasonably sure the problem is in the front harness. You should stop by your LBS and see if they have one they'd let you plug in to test your bike.

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Sorry, but my bet is still on that main connector just back of that front control box jb. If it was in the front ahead of that control box jb, then it would only affect the fd or rd, depending on which side is broken, since the signals from the left and right shifters are combined at the control box jb. But maybe we are agreeing and just describing things with different words. In any case, I've seen this specific symptom when that front big connector comes adrift. Usually its because the cable was installed too short, and when the handlebar is turned, it pops the connector out a bit.

Sorry if there's a misunderstanding. I think the problem is with the front harness, but not necessarily in front of the junction box. Probably in the junction box or with the connection to the rear harness somewhere.

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Ok. Agreed. You know, there's a theory in science that I think is called "Ocam's Razor". In essence, when you're faced with a problem, its usually the simplest solution that is the answer. That's why I keep thinking its that front connector. But I agree with you that that's the area of concern. Thxs.

Thanks a lot for the nice replies.

I have ordered a new front harness, since no LBS near by had one I could use for testing.

I"ll get back in a few days.

So, you tried unplugging and then reconnecting that front connector, and that didn't fix it?

I did. I have two rear harness and one front harness. Tried both combinations.

Today I installed a new front harness, and problem solved.

Thanks for your replies.......