I think I will add a hidden white/blue “choke switch direct to carburetter solenoid” wire into this supplementary loom through C5258 . Firstly because I have a neat choke switch preinstalled by a PO on the dash (see Growler’s photo 679265 with white arrow above in this thread) and it will give me more control over the carb solenoid. Secondly because the permanently live carb solenoid is a ? fire risk. Thirdly because it won’t show in a new loom.
Not being at all certain that the general loom makers will have enough information to make this loom, I’ve got so far that I am thinking that I will put the wires together myself. Then to get that professional look to match the rest of the car, send it off for it to be professionally bound with the rest of that being made for the car.
Can anyone post any original photos of how the wire to the oil sump unit is fixed so that it didn’t wave around in the breeze?
As an aide to getting the wiring associated with the “Petrol gauge & reserve warning light”, the “petrol oil switch” and the “oil sump unit” on the XK 120 LHD FHC into the harness as depicted in Lucas Wiring diagram W94602, attached is a diagram extracted from W94602.W94602 petrol gauge, etc.pdf (171.2 KB)
Thank you Simon, my new harness did not include the sump oil level sender wiring and this is a remaining detail that I am addressing on FHC 679924.
Tom Brady
Hi Tom,
Delighted to make contact.
The question I have yet to confirm is the actual routing of the oil sump level wiring.
I have asked the folk making my new harness to do the following:
1. A green blue in the harness from instrument panel ( petrol
oil switch) to Regulator unit.
2. A green
blue in the harness from the Regulator unit to the “coil, distributor, carb solenoid and thermo unit”.
My plan is then to bring harness no. 2 above to
C5258 then make my own harness from there.
If
you have anything to add to this theory I would be interested to hear from you again.
Kind
regards,
Simon
Simon,
I do not know the correct routing of the oil switch wiring but my August 52 FHC does not have the C.5258 junction box. My idea is to run a Green Blue wire directly from the oil sump sender to the back of the terminal on the level gage, passing through the same hole that the gas sender wire goes through. It would be much appreciated if anyone has an original wiring setup for the oil sender wiring and could comment.
In the absence of any response to Tom, since I am only in the process of finalising the specification of a new harness, I am going to add the green blue oil switch wiring in to the harness from the instrument panel to the control box then add a further green blue in the harness from the control box to the coil. Although this is a bit of a detour it is neatly hidden away in the harnesses and avoids individual wires running across the engine bay. An alternative to taking the lead on its own through the gas sender wire would be to use the large hole behind the windscreen wiper motor which tucks it away more easily.
Returning to the post C5258 junction box harness, the first port of call after C5258 is the carburettor solenoid, not the coil as in Lucas wiring diagram W94602.
Accordingly I have attached a not to scale drawing showing the dimensions required for the supplementary harness although I will report back whether this needs to be amended after fitting.Harness for junction box C5258 with dimensions.pdf (532.7 KB)
Just letting you know I am eagerly collecting this information, as I will be rewiring mine in the next few weeks. I have removed my PO created wiring and am now working on the black paint on the firewall. I wonder what size brush to use. 
I had made this diagram years ago.
using this photo.
Most reassuring that I have come to the same solution as your goodself.
How are you going to make the joint buried in the braiding where the white lead splits to the carb solenoid and the coil?
Thinking about it, I am inclined to believe that a soldered joint buried in braiding would not be a standard practice with Lucas.
This C5260 or Lucas 997701 harness was a low production item only used in a small number of 120s, and I don’t even know if the photo of the harness I posted is all that accurate a representation, but it’s the only one I’ve ever found.
So I think it was probably two white wires, one from coil to solenoid and the other from junction box to coil.
