It's even funnier on YouTube (see below): He grabs the battery drill and mills a neat hole in the down tube, making the cable sheath easily accessible. In reality, however, the cursed inlets and outlets are not the size of a coffee cup saucer. Instead, they are so tiny that it can be a fiddle to squeeze through an outer sleeve with an end sleeve.

Simply pulling in a cable takes time...

I recently had the task of fitting a trail-compatible light to a motorized mountain bike. Connected directly to the battery - a fine, integrated thing. The light was quickly fitted under the display and needs to be connected to the motor in order to provide light. To do this, the cable has to go through the down tube; access is via a rather tiny hole on the right-hand side of the upper down tube.

This is how the dreaded process begins, which has absolutely nothing to do with mechatronics or mechanics. More like caving and nerve and finger acrobatics. So I push the Lupine's power cable into this access hole. And poke and poke. The crucial question: will the cable come out at its destination? It could be that the manufacturer has installed a cable duct and the cable has no choice but to see daylight again in the right place.

... more than one nerve-wracking hour

Just under 65 minutes later, the cable actually comes out in the right place. To do this, I removed the mid-motor, dismantled the chain guide, removed the battery and uncovered a cable duct underneath. Then, using the special tool from Park Tool, I first tried to clear a path for the cable. I fiddled around with magnets on the down tube while holding the flashlight - maneuvering several tools at the same time like an octopus and (almost) never losing my nerve.

In the end, it's a mundane, steel brake cable that finds the right way in and out again. Of course, only when it is bent into a specific angle after a centimeter in length so that it doesn't get stuck at the exit. I use gaffa tape to fix the light wire to this brake cable, which has been pulled in as a guide, so that the cable can be pulled in. I connect the cable to the light input on the motor, attach the negative and positive poles to the light and - oh wonder - the light does its job. The late joy of the light is great. And my disbelief towards these bike designers who design something so complicated and unleash it on mountain bikers and mechanics is even greater.

A few tips for internal cabling:

• When you pull out a cable: always pull one out straight away. For example, attach the Park Tool lance to the brake line, carefully pull out the brake line and then you have the blue cable internally routed to pull in the new line.
• If this is not possible with the special blue tool: Attach a movable light cable to the cover using strong adhesive tape. Then very carefully pull out the cover, if there is resistance try to explain why the removal maneuver is stalling. And don't be surprised if the adhesive connection tears off despite all your care. There are simply frame and rear frame constructions that are not made for retrofitting cables or outer sheaths.
There are plenty of "Bike Hacks for Internal Routing" or "How to fit internal cables": Search for these terms on YouTube. You'll find everything from professional to very amateurish instructions on how to fit cables. It's even about vacuum cleaners!
• As mentioned above, the special tool from Park Tool is recommended for successful internal cabling. A flashlight is also important to shed light on the fork, frame or rear triangle. If necessary, the LED light from your smartphone will also do. Shine it in at the entrance and look at the exit to see which way a cover has to go. Sometimes this visualizes an amazingly acrobatic path.
The best recipe for stress-free work on internal cabling is and remains No time pressure and as good a mood as possible. If you start fiddling around under time pressure or in a bad mood right from the start, you've already lost.
• What sometimes also works wonders - before you actually drill a hole in the carbon frame like the YouTube mechanic: Put the bike in the corner. And tackle the repair again a day later, because after all, good things take time. Maybe write a message to the manufacturer in a quiet minute to say that the bike is a lot of fun to ride, but a nightmare in the workshop thanks to the poorly installed internal wiring.