I've decided that all the wires will be marked.

I tried to come up with a simple method. I first separated the whole wiring in subsystems designated by a letter : B for battery and alternator, E for EFIS..Then, each part in the circuit gets numbered with that letter: B01 for the main battery, B07 for the alternator, B15 for the starter relay...Each wire is named after its originating and destination element : B01B03 for the wire from battery to battery relay.If there is more than one cable from one item to another, the discrimination is done by color or by adding some supplemental information.

The Excel file at the end of the article helps managing all this.The first two columns are for the reference and the name of the element. (Those two columns need to be ordered by ascending reference for the worksheet to work). The next columns create the cable names once the departing and arriving points are entered in the coloured columns. The last columns compute the cable name, a name for the origin and a name for other end. The sup column allows to enter some other info (a, b... in case of cables with same name).

Once this is done, the second page can be used to print out the labels. There will be a two cell label for each end and a four cell label for in between. Once cut, the labels are heatshrinked to the cable with clear heatshrink. This is a example for the EFIS system. There are two elements E18 and E19.




The wires are marked as follows.
The E01E18 label indicates the wire goes from E01 (EFIS1) to E18 (magnetometer 1). The other label has the "> E18" information which indicates that the end of the wire gets connected to E18 item.




For an easier identification of the connectors I added a label with the item they get connected too.