Forget about the chassis earthWhen I read the following this morning, it made complete sense: "The easiest way to do this is to tape some suitable thin section wire to the new curtain wire liner, before you thread it through." But subsequently having looked at the trunk, I realised I would not be able to get the wire past the liner collet, and it would also be difficult at the torch end. As an experiment, I pulled back the large rubber sleeve on the trunk, - and was pleased to find the other end of the white wire there (I was due some good luck :-) )
I think in car terms of a "positive or negative earth chassis" - so perhaps when I see the new photos from DSR (thank you), it will become clearer, but at the moment the main brass fitting of the trunk is bolted to the chassis and that connection includes the large ring connector. Will I continue to bolt the trunk to the chassis but omit the ring connector?
Normally the case of the welder will be connected to the mains input earth (the big pin on the 3 pin plug) but the output welding current will be isolated from the chassis. Check with a meter and you will find that the earth clamp isn't connected to the chassis and the torch isn't either. The wire drive itself is mounted on plastic insulators and is not connected to the chassis either. Basically, the whole welding current side of the system is floating away from the chassis. You have to maintain this isolation whenever you modify the welder.
If the chassis was connected to mains earth and you failed to notice that you hadn't clamped the welding earth clamp to the job or it wasn't making good contact, there is a risk that you could send welding current along through the mains cable to the job if the job was connected to the mains earth - this is quite possible if you are welding on something like a drill or milling table.
Bit off topic, my Cytringan Bantam welder is built so that the case is connected to the mains and is also the welding earth.