Cutting the wires - what could go wrong?
 

At each side of my bonnet I have 4 wires coming from the lights back into the car. I am guessing that each side there is a wire for Indication, Sidelight, Headlight and Main Beam.

To make my bonnets easy to swap I want to fit a single 4 way connector to each set of wires. I don't know which wire does what and they disappear inside bits of the bonnet so I cannot easily trace them.

I don't really need to know which wire does what to fit the connector for the existing bonnet. I just make sure that the 2 cut pieces for each wire are connected together afterwards. For the new bonnet I will need to know the order though.

My plan to identify which wire is which is as follows:

1) With the current bonnet in place check all the lights work.
2) Cut one wire and see what doesn't work. Label that wire accordingly
3) Repeat for the remaining wires until nothing works and all 4 wires are labelled
4) Fit connectors and wire them according to labels for existing bonnet
5) Check everything still works

rest

6) Fit wiring to new bonnet and label all the wires
7) Fit the connector with the labelled wires in the same order as the old ones
8) Fit the bonnet, connect up and check it all works

Anything wrong with the plan?

In the absence of a voltmeter, that's the way I'd do it.

Where does the electrical earth to the grp-mounted devices come from?

Ian - you beat me to it!

no problem for me...... the wife says I am permanently grounded

Earthed against the bonnet pins + Bonnet frame + hinges.

Mine still has the framework of the original bonnet in it.

I added the wire to the hinges after my previous electrical challenges suggested the other two weren't working correctly. It turned out the wire to the bonnet frame was loose and the bonnet pins work perfectly when stationary. Unfortunately the bonnet bounces slightly on bumpy roads and the lights kept turning off which was fun.

I shall now spend my lunch hour cutting wires. If you hear a BOOM!!! from Southampton you know I cut the wrong one

I am getting well pissed off with being on crutches and how much it slows me down. Do you want to know what I have achieved since my last post 1/2 an hour ago?

Opened the bonnet on the Barchetta
Got the tools and electrical connectors ready
Got wet as it started to tip it down and I put everything back

Grrr!

What could possibly go wrong?

Apart from the obvious finger snipping you could..
Blow fuses
Mark the wires and the markers fall off
Find you are cutting wires for the ecu instead
Get halfway through and darkness falls