Fun fact, since I have decided to move the coil to the top side of the engine cam cover height on right side, I can see that the original wiring will not be long enough. Here is what I noticed, the harness coming through the bulkhead that goes to the oil temperature (assumed) the coil and the starter push on the carburetor. I can splice new wire at the bulkhead or splice into the existing wires which have the coating missing in places and the wire showing. I could also buy whatever wiring harness and replace it all together. This last option I refuse. Not going there.
So the question is replace from bulkhead or add to existing wire?
splice closer to coil or at end…wherever easiest to get to…use proper connectors, not just a twiste of wires,and if you have the right size heat shrink wrap tube…and heat gun to seal it , it will look neat. Nick (the standard top of carb location is just fine.)
Guess what, the factory realized this too.
For a few months Nov '51 to Feb '52 they ran a short extension harness from a Lucas junction box on the firewall (scuttle). This was a topic we hashed around many years ago. Mine is 679187 and has it.
Following these entries in the SPC, it would appear that only LHD cars had it, and they weren’t making any RHDs at that time.
Although now I see by your chassis number that you should have the coil on top already and the later harness which is long enough. Unless your coil was moved and the wiring shortened.
Rob,
The coil was mounted on the inner fender on the right side. When I got the car. I suppose if the correct wiring was there before it isn’t now. I don’t mind making a small length of wiring harness. I made many such harnesses for the Silver Cloud III. I use the connectors but remove the colored plastic and use shrink tubing to make the wiring neat. I will make up what I need as soon as I understand what wires go where.
Maddy
I am working on the XK120 FHC wiring which is + ground. Some original wires are pretty hard so the insulation just flakes off when moving the wire. Using the electrical diagram in the manual, I have patched onto the wire coming from the control box A3 with a white wire leading to the carburetor solenoid which then goes to the SW side of the coil. The other terminal on the carburetor solenoid has a white with black wire leading to the thermostat unit and from there a black wire to ground.
Here is where I become confused, the white with black wire from the carburetor solenoid going to the thermostat. What is this about? I do not see a terminal on the thermostat housing nor any where else on the cooling system for that mater.
Does anyone have a description of this wiring or pictures to show the wiring? Thanks!
White from carb solenoid to SW or - on the coil, or going over to A3 is also correct but you already should have a white from SW to A3.
Black from carb solenoid to the otter thermal switch in the top hose elbow (if it works) and not to ground. This switches on when the water is cold and off when it warms up (sometimes).
OR black from carb solenoid to a manual switch located inside where you can switch it off when you want. The other side of the manual switch would be grounded.
White with black from the CB or + on the coil to the side of the distributor, and not ground.
The original wire from A3 is white but after 68 years looks more like a creamy brown. What is the thermostat the one needing a terminal? I can get a better picture but for now it the thermostat the item located in the bottom right of this picture? If so how is a terminal affixed to it?
meaning that which is in your “better picture” is not the thermostat, nor the thermostat housing area…it is called the otter switch…it is a heat switch that controls the cold start carb on/off via water temp. Many by pass it as they are prone to run too long or not enuf, or malfunction entirely, so disconnect it and just hook up wires to a hidden switch on the dash…on for cold start…then off. But in stock format the wires to it control the start carb, as Rob R described. Nick
I had my suspicions, Rob, that is the switch you referred to. I removed that piece of coolant conduit the otter switch was on. There was only 1 bolt of the 3 holding the otter switch. The remaining one turned but broke off in the housing. I suspect I’ll have to drill that out and re-tap. Whatever is inside that otter switch where the wire goes I am unsure it would even function. Is there a way to test it?
Perhaps just purchase a newer one is the solution. Thanks Rob for your help.
Maddy, replacement Otter switches are expensive and never worked that well to begin with. I suspect half of XK Jaguars have a cheap bypass switch mounted under the dashboard to more precisely control the off and on of the starter carb solenoid. My XK120 does.
Exact replacements for the broken Otter switch hex head setscrews are available through Moss Motors under part number C7134/1R. I’ve had good luck removing broken-off setscrews by having my machinist weld a nut to what’s left of the screw shank and then carefully backing them out.
The Otter switch is simple and easy to repair. Remove the metal bulb and you will see a bimetallic switch. The switch contacts can be bent such that the contacts open at the correct temp. Mine works correctly but I also have a hidden (from the Concours judges) bypass switch.
Thanks, Mike. I see a replacement otter switch is just over $100 and if it fails as often as posted it is not a wise purchase. This explains why there was no wire going there. I will look for an existing switch in the cab in case a previous owner installed one for the starting carb.
Good information from all who replied thank you all so much!
if there are wires on the start carb solenoid follow them back to where-ever they goes…and you can check when a suspect is found with a continuity tester. (ign power off). The start carb solenoid can be tested…they too fail often…another $100 or more part…but this one needed for cold starts. Service Manual pages C14-15-16.
Nick
Just postpone the restoration of the Otter Switch until you’ve got the engine running.
It is absolutely possible to get the Otter Switch working again but you’ll have to take it apart. After all, it’s just another bi-metal switch that has to be calibrated (meaning carefully bent in the right position). Mine have always worked and switch off the choke function when the cooling fluid reaches 35 C. See pictures.
