check out bettershifting.com - read through some of that page and you should have a clearer understanding of what you do (and don't) need. It helped me a fair bit.

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My Blog - http://leegoocrap.blogspot.com

There are a bunch of threads about it but here is a basic diagram showing the internal or external options for the Junction A. Wire sizes vary, below worked for my P3 which is a 2018 61cm. Bettershifting.com is also a good resource. Cheapest way to do it is used obviously, I've seen some decent used sets for around $700 or so, usually doesn't include the battery charger though. I got majority of a set (brifters, battery, RD, FD, charger, JA, JB, wires) for I think $550, then shopped around for bar end shifters, wireless unit and JA/JB that I needed. Lots of different ways to route the wires, pretty much as long as you have the components wired to a battery you can make it work in a variation of ways.

Fantastic start. Thanks to both. A bit vague on the Junction A position. Internal or External?

Depends on which type of A Junction you use.

See? I didn't even realize there were different ones. Surely there is a list/diagram of the components that were sold on the 2018 P3. It was an option I couldn't afford at the time, but it existed, so why re-invent it? I'm good with a wrench, if I have directions to follow.

Here’s my detailed Di2 upgrade. They have two junction A boxes. The normal one that is typically attached externally at the cockpit in most bikes. And the bar-end version that I used. That is meant for road bike bars, but it is easy to adapt toTT extensions.

https://forum.slowtwitch.com/forum/Slowtwitch_Forums_C1/Triathlon_Forum_F1/Di2_Detailed_Upgrade_Write-Up_(Felt_IA16)_P6572184

I have just done my P3.

I have the bar end jct A in the left hand aero bar. I have a junction B in the stem and another one in the bottom bracket end.

Its turned out really neat using PD Aeria bars and stem.

I bought most of my kit second hand off ebay keep costs down.

shifter buttons on the base bar set up as per my road bikes with rear mech on right up and down and frt mech on the left.

I have my di2 set up in semi synchro mode which means the frt mech shifts automatically when it gets to a particular cog on the rear.
This means on the aerobar my right button moves to a harder gear and left moves easier. i then use the second buttons to control my garmin.

Here you go.... 2016 Di2 specs. Note that it came with the external battery and did not include the wireless unit. I have the internal battery in the seatpost and wireless unit in the down tube. Also needed longer wires to connect to the brake levers.

“specs from our current (2016) P3 Di2 which has the new synchro specific shifters on both the extensions and the basebars.

1x FD-R8050 (Front Derailleur)
1x RD-R8050 (Rear Derailleur)
1x Pair ST-R8060 (Basebar Shift/Brake Lever)
1x Pair SW-R9160 (Extension Shift Switches)
1x SM-EW90-B (5 port A Junction)
1x SM-JC41 (B Junction)
2x EW-SD50-I 250mm (Wires)
3x EW-SD50-I 600mm (Wires)
2x EW-SD50-I 300mm (Wires)
1x EW-SD50-I 1000mm (Wires)
1x BM-DN100-S (External Battery Mount Short)
1x SM-BTR1 (External Battery)
1x SM-BCR1 (External Battery Charger)
1x SM-BCC1-2 (External Battery Charger Cable USA plug)

It's possible to substitute the internal battery (BT-DN110) and charger (SM-BCR2) but the frame isn't specifically designed for it. You can install it in the Seatube wrapped in foam to prevent it from moving around.

You could also substitute the older ST 6871 brake/shift lever and SW-R671 Shift switches if you want to be able to shift in conventional mode as well.

For installation there is no need to remove the crank since the BB sleeve is closed. You can route the wires using the opening under the BB. “

Close, but is the 2016 and 2018 the same?


A little more homework done. Looks like I "may" be able to mount the battery inside the bottom tube, just forward of the BB. This was per a P3X manual I found. Cervelo came back with an apology, but no documentation was available on the 2018 P3, Di2 install or parts....
I called 3 shops, including 2 that were Cervelo specific. None could answer "where does the front junction box go?"
The information you guys have supplied so far has me convinced that I can do this. But the lack of an official diagram has me concerned to start. I'm looking for a factory-type upgrade, not a full conversion of something that hasn't been done before. And I certainly don't want to double the cost by getting a whole new cockpit.

I will have 4 wires up front that need to get down to the BB. Surely I don't just run all 4 together. And where is the charging port? Man, I wish I could just find some pictures of this year/model.

can i ask where this part is mounted?

I have the external junction box mounted to the side of stem with the rubber band thingie In a position where it’s mostly shielded behind the PD aerobar bracket (narrow aerobar setup). If I were to do this again I’d use the EW-RS910 internal junction box mounted in the end of one of the aerobars along with a SM-JC41 junction box.

I looked for the dimensions of the RS-910 to see if it would fit on the end of my extension bars (where the current shifter cable exits). That seems important to know.
And, if you did it, where would you put that JC41? I would guess just behind the stem in the hole where my current cables enter the frame?

If you go internal Junction A (does fit on standard Profile Design bar extensions) you may want to put the JC41 (junction B) inside your base bar, you have to kind of fish it in there. If you want to go complete internal you have to really think about how the bar end shifter wires get down to the base bar, unless you have hollow spacers or a front end that is more setup for it naturally. By having the JC41 in the base bar you're only carrying one wire over the stem to the front tube and you can tape or heat shrink that one wire to the brake cable going to your rear brake to keep it even cleaner.

There are probably at least three places you could hide an internal battery. Just be creative.

No one can tell you how to wire everything because it depends on the specific aero bars, base bar, and stem that you have on your bike, and the way that you want it to look.

The location of the A Junction depends on which A Junction you have, where it will fit, and how you want the bike to look.

If you have four wires in the front of the bike, you can connect them together in the front and run one wire toward the back, and then connect the front derailleur, rear derailleur, and battery.

The location of the charging port depends on where you put the A Junction.

I started with an assumption. Since Di2 was offered on my model when I bought it, I could just copy that. Different places to hide the battery, multiple options for junctions and how I want it to look.
Frankly I want it to look like I bought it that way in 2018.
Setting all that aside, I can see this is a fun and creative project and I may want to widen my scope.
Later I'll take a few pictures (I suck at posting pics) and ask for more specific advice. I don't think my original thought of "stock" is going to work out the way I hoped.

what is this bolt for?



I assume these bolts on the bottom are for holding a battery. But I'm not sure how I would slide that in, with the sealed bottom bracket.



I did find this picture of a 2019 P3, so at least it seems likely that stock meant external Junction A.

Am I on the right track here?

Hi! :)

Those bolts on the bottom can probably be used to mount the external battery mount (BM-DN100 is the current model, SM-BMR2 the previous). The battery itself is SM-BTR1.

And yeah, that junction as can be seen in your second image is the SM-EW90-B (5 ports).

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BetterShifting.com - Di2 help and guides| BetterShifting Instagram | Terry's Instagram

I upgrade my P3 to Di2. While I can appreciate the confusion when getting started, it's really straight forward to do. If you can wire up a home theatre system, you got this.

The internal battery is super easy to hide in the seat tube. No need for fancy holders. Simply wrap the top and bottom of the battery with some foam to reduce bumping around (or rattling) and place it down the seat tube. I also taped a small length of an old shifter cable to the end of it so that I can easily pull it out of the down tube if need be.

If you want shifters on both the brakes and extensions, you'll need a 5 port external junction box. Unfortunately, the bar plug junction boxes are restricted in size and only has 2 e-tube connection ports (one 'in' and one 'out') and is simply not enough to connect all shifting points.

The external junction box can be routed where ever you like. I put a bento box on the top tube and found that I could easily tuck the junction box in there. My bars (tririg alpha one) hide all the Di2 e-tube wires so the are barely visible at all.

the rear brake cable and e-tube wire can easily be routed through the top tube. Looks pretty clean and I highly recommend.

If you need pictures, let me know.

"If you want shifters on both the brakes and extensions, you'll need a 5 port external junction box".

Not true. You can join everything with a B Junction.

I guess you’d need 2 ‘b’ junctions and and an ‘a’ junction to go that router.

There is actually a 6 port junction b available if you pull it from the xtr external battery mount for internal batteries. It is fairly large min diameter so it can be a bit more difficult to hide internally.

True.. the SM-BTC1 has a 6 port splitter / junction.
I think it'd be cheaper to buy two SM-JC41s and just tape them together though.. and smaller too.

But yes, it is an option and it works for some, sure.

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BetterShifting.com - Di2 help and guides| BetterShifting Instagram | Terry's Instagram

You guys are all being really helpful, and I appreciate it. I finally got helpful feedback from Cervelo. To put the battery in the seat post, I can use the MT-BINT-SP, or just foam as mentioned above. I REALLY like the tip of attaching wire to pull it back out later.
I have decided to simply mount the 5-port junction to my stem and call it good. Not as streamlined as some other options, but keeps me from drilling holes, for now.
Big money is not in the junction boxes, and if I end up with an extra, I can resell.
Do I start internet shopping for individual parts, or look for some upgrade kits? Pretty much decided to go single-button, full synchro, with Ultegra parts.

If you jam the battery inside the seatpost, you don't need to attach an extra wire to pull the battery out of the frame.

If you want to keep everything internal, you might not have to drill any holes.