Originally Posted by TFeeney
At the end though, what has me the most nervous up to this point is the ribbon/tape layout you did on the bench. I've got a mockup of cardboard, but I wonder how accurate the measurements you took have to be?
After all the work to create a beautiful harness, I can see myself installing on the airplane and being 1/2 inch short on one connector. I understand the concept of service loops, but can you explain how you incorporated them - I think the slack in the system is my answer, but I can't visualize it in the picture below.
I used ribbon because it was at hand and easy to tape together. It is the 1/4" kind that makes curly decorations. I taped the ribbon in the location I wanted the main harness section first. That's the part where everything else branches off. Next I taped in position lengths of ribbon where I envisioned a branch coming off. For the service loop, as an example, I plan on servicing everything through the PFD/MFD hole. They will need to be easily removed. So I need a branch that not only reaches the device, but allows me to remove the PFD and put it away far enough to get at the connectors in the back. No crawling under the panel to disconnect the connectors.
Once I have enough length to reach the component, then I allow enough slack to move the component into a position to access the connectors. I then clipped the ribbon to length and taped it to the back of the mock device. I also taped the ribbon in the position I intended to route/fasten the harness permanently.
Some components needed service loops, some only comfortable slack to allow the connectors movement during service. Once I had the entire harness made of ribbon complete, I pulled it carefully out and measured it. What you see in the diagram is the actual length of the ribbon between branches and to each device including the service loop length.
I had tried to measure with a tape measure before I hit on this method, and well, it would have been an expensive mistake .... lots of incorrect measurements.
I also purposely went a little on the long side any time I wasn't positive of the position or routing. Easy to cut, impossible to lengthen. Everything fit well in the end