dag019 said:

I invested in a proper barrel crimper so you can use "factory" brass crimp connectors rather than the red/blue/yellow crimps you see everywhere else. This is the tool that I have LINK with jaw H for open barrel crimps

I then just ordered a whole lot of the brass double barrel crimp connectors and the little insulated covers for them. I use a quick online tools to convert watts to amps for my lighting circuits, and knew from experience the twin fan setup I have needs 20amp on start up for each fan from when I was initially installing and it kept blowing fuses. It used less to run but has a spike to start.

I got my coloured wiring from this chap on ebay (LINK) as he did the normal colours and had enough that I could then use different colours for additional things which I then recorded for future use.

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Thanks -- those are useful links. Do you have a link/pic for the brass crimp connectors please?

jwrw said:

I've got various wiring diagrams but of course they don't show you where the wires should actually run, or what gauge they should be, or what connectors they have on them. I'd love to find some photos of a decent job done by somebody who knew what they were doing.

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I am not saying it is a decent job (although I like to think it is) or that I am am expert but know reasonably well what I am doing. I catalogued a lot of the standard wiring and my additional wiring in my rebuild thread after the fire LINK. It will not be exactly the same as yours as I fitted the later 300tdi looms throughout out but it may help with giving a better idea of where things should go.
Again for the 300tdi I used this website as a bit great resource but not sure how good it is for other models: LINK. On a quick look there does not seem to be the same connector library and search by wiring colour for the earlier models but still a good resource.

jwrw said:

Yes, that makes sense. But I don't really have much sense of what 'small cable' and 'large cable' means. All the wires at the moment are thin. But I looked at a calculator website which suggested that for 15A (purely a guess on my part -- that's half of the 30A fuse rating recommended by Kenlow) it would need 3mm or 4mm conductors -- which is at least 3x the size of anything installed at the moment!

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Remember wire size is given as an area rather than a diameter. So 4mm wire is a 4mm square cross-section not 4mm diameter. You want the fuse to be the smallest rated thing in the circuit so it blows before any damage is done. For example the ebay wire link I gave on my previous post is 1mm square wire which is physically small and is rated to 16.5amps, but I have used this on my circuits with a 10amp fuse so there is no risk of any damage as the fuse will blow well before the limit of anything else. This is what I would be counting as small cable and is for low amp circuits that switch a relay.
Looking at your pictures I would guess the red wire you have currently is the 27amp 2.5mm square and readily available from most motor factors. This is what I would be considering as larger cable to actually run the additional items (lights, fans etc). However if you need a 30amp fuse you will need a higher than 30amp cable. I used 4.5mm square 42amp cable for the relay to fan power feed during my rebuild and similar to you had a 30 amp fuse.

jwrw said:

Thanks -- those are useful links. Do you have a link/pic for the brass crimp connectors please?

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LINK these are the spade connectors and insulators I used with the barrel crimping tool linked earlier but there are lots of others available. The important part is that they are the plain brass open crimp rather than the tube style crimps so when completed you get a connector that looks the same as the factory ones with the exposed wire tightly crimped and the full insulated wire also tightly crimped into the connector