Thanks for all the response to my incomplete posting about the wiring harness replacement; I lost control of an archive query and dispatched early.
The car is 67 FHC 1E33369, 4.2 Ltr. LHD with horns on the picture frame. It definitely needs alternator and engine bay (Forward harness in the parts manual) harnesses. These enter the bulkhead on the left side above the battery.
To properly paint the engine bay, I plan to withdraw the harness into the cockpit but not disconnect from the fuse boxes and dashboard until I am ready to replace the harness. Should I worry about this or just strip it out, and assume there will be adequate documentation from a vendor (or assistance from the forum) to properly install a new one?
Can the forward bonnet harness (lights) be removed / installed without dismantling the bonnet?
The body harnesses seem to be in good shape: is there some inspection of these that is recommended?
There are 2 approaches I know of if the harness is to be replaced and not reconnected.
Cut instrument and switch leads leaving enough wire to identify colour, which you can use as a reference to connect a new harness. Or remove wiring at terminals, make sketch of each instrument and switch wire and connection as you go, and withdraw harness towards engine bay complete with terminals and connectors. Took that approach on 1E31711 to replace a literally baked front harness in a car originally delivered to California. The complete original harness will be a good guide to what should be in the new harness and will help identify any minor discrepancies such as the location of a fan relay previously added to my car. The dash top has to come off, and I left a pull cord behind the dash from the passenger side to the bulkhead opening and used it to pull the new harness into place. Slow process with multiple groups of leads to route but relatively low on the difficulty index.
Harness will not likely come with any documentation. Wiring diagrams are in the service manuals and the standard British wiring colours keep it simple. Don’t forget the sketches.
Headlamp wiring is accessible after removing sugar scoops. Bonnet connection and terminal block is on driver’s side and I believe leads to passenger side can be pulled through assembled bonnet.
You can check existing harness for resistance and continuity with a meter, and may find corrosion at connections that can be cleaned up, but It doesn’t take much in the way of previous repairs or tired wiring to justify the relatively low cost of a new harness.
I replaced my bonnet harness on 1E33801 not long ago and since I am having the entire car painted now I have purchased a new forward harness. The Autosparks website ( https://www.autosparks.co.uk/finder ) gives the most complete listing of the harness needed that I have found. Rhode Island Wiring provides a hardcopy list of all the connections and that’s why I ordered my engine bay harness from them. I kept the 3AW. The harness inside the bonnet is very straightforward as mentioned and I got that from SNG. Cutting the leads near the connection with enough wire to identify the color is a good way to make sure you are connecting the new harness properly. Rhode Island Wiring had me send them the bonnet plug and they wired up the new harness to that which was very helpful. Take lots of photos prior.